'Climate  - 

Considered  Especially  in  Relation  to  Man 


Robert  DeCourcy  Ward 

Professor  of  Climatology  in  Harvard  University 


Edition,  Revised 
Illustrated 


G.  P.  PUTNAM'S  SONS 
NEW  YORK  AND  LONDON 

fmicfcerbocfter  {press 
><     1918 


NU 
\c\\1 


COPYRIGHT,  1908 

BY 
G.  P.  PUTNAM'S  SONS 

COPYRIGHT,  1918 

BY 
G.  P.  PUTNAM'S  SONS 

Revised  Edition 


Ube  Ymicfeerbocfcer  press,  Hew 


PREFACE 

TTHE  preparation  of  a  volume  on  Climate  for  The 
*  Science  Series  was  suggested  to  me  by  the 
Editors  in  October,  1904.  I  was  asked  to  prepare  a 
book  "  which  can  be  read  by  an  intelligent  person  who 
has  not  had  special  or  extended  training  in  the  tech- 
nicalities of  the  science,  .  .  .  the  book  to  be  such 
as  would  not  compete  with  strictly  meteorological 
text-books,  but  to  handle  the  broad  questions  of 
climate."  It  so  happened  that  it  was  then  already  in 
my  mind  to  prepare  a  book  dealing  with  certain  large 
relations  of  climate,  which  might  serve  as  supple- 
mentary reading  for  the  students  in  my  course  on 
General  Climatology  in  Harvard  University.  The 
present  volume  is  an  attempt  on  my  part  to  write 
a  book  which  shall  meet  the  wishes  of  the  Editors  of 
The  Science  Series  and  at  the  same  time  fit  the  needs 
of  my  students. 

Climate  is  based  on  lecture-notes  which  have  been 
accumulating  for  the  past  ten  years.  It  does  not 
attempt  to  present  any  very  new  or  original  material, 
but  it  does  aim  to  co-ordinate  and  to  set  forth  clearty 
and  systematically  the  broader  facts  of  climate  in 
such  a  way  that,  as  desired  by  the  Editors,  the  gen- 
eral reader,  although  not  trained  "  in  the  technicali- 
ties of  the  science,"  may  find  it  easy  to  appreciate 

iii 


iv  PREFACE 

them.  At  the  same  time,  the  needs  of  the  teacher 
and  student  have  been  kept  constantly  in  mind,  and 
the  subject-matter  has  been  arranged  in  such  a  way 
as  seems  best  to  adapt  it  for  purposes  of  thorough 
study. 

Climate  may  be  considered  in  a  way  as  supplement- 
ing the  first  volume  of  Dr.  Julius  Kami's  Handbuch 
der  Klimatologie,  an  English  translation  of  which 
was  prepared  by  me  and  published  in  1903.  In  that 
book,  the  standard  work  of  its  kind  in  the  world,  the 
principles  of  climatology  are  clearly  set  forth.  My 
present  volume  deals  with  matters  which  are  either 
omitted  altogether  in  the  Handbook,  or  else  are  very 
briefly  treated  therein.  Climate  is  wholly  independ- 
ent of  Hann's  splendid  work,  except  in  so  far  as  my 
study  of  that  book  inspired  me  to  prepare  this  one. 

The  general  scope  and  purpose  of  the  different  sec- 
tions in  Climate  are  as  follows.  The  Introduction 
is  essentially  a  very  condensed  synopsis  of  the  first 
six  chapters  of  Hann's  first  volume,  with  the  addition 
of  some  other  matter.  Chapter  I  gives  a  sketch  of 
the  classification  of  the  zones.  Chapters  II  and  III 
give  a  brief  summary  of  the  general  climatic  types 
which  result  from  the  control  of  land  and  water,  and 
of  altitude,  over  the  more  important  elements  of 
climate.  Chapters  IV,  V,  and  VI  are  intended  to 
give  an  outline  of  the  climatic  characteristics  of  the 
zones  in  a  simple  and  vivid  form,  with  the  least  pos- 
sible use  of  tabular  matter.  For  further  general  in- 
formation on  this  subject,  reference  may  be  made  to 


PREFACE  v 

the  world-charts  of  temperature,  winds,  cloudiness, 
rainfall,  etc.,  given  with  greater  or  less  completeness 
in  the  various  text-books  of  meteorology,  and,  very 
fully,  in  the  Atlas  of  Meteorology.  In  Chapter  VII 
the  attempt  is  made  to  give  a  survey  of  some  of  the  re- 
lations between  weather  and  climate  and  a  few  of  the 
more  important  diseases.  Little  information  on  this 
subject  is  readily  accessible  to  the  general  reader. 
The  life  of  man  in  the  tropics,  the  temperate  zones, 
and  the  polar  zones  is  considered  in  Chapters  VIII 
to  X.  No  attempt  has  been  made  to  discuss  this 
subject  in  detail,  for  to  do  so  would  far  exceed  the 
limits  set  for  this  book.  It  has  rather  been  my  plan 
to  pick  out  typical  illustrations  here  and  there,  as 
suggestions.  Many  of  the  cases  referred  to  will 
probably  be  familiar  to  teachers  and  students  of 
geography,  but  the  co-ordination  of  all  the  examples 
by  climatic  zones  and  by  the  natural  climatic  sub- 
divisions of  these  zones  will,  it  is  hoped,  tend  to  give 
adequate  emphasis  to  the  climatic  factor,  which  has 
hitherto  been  much  neglected.  The  final  chapter,  on 
changes  of  climate,  deals  with  historic  and  periodic, 
and  not  with  geologic  changes.  The  last  phase 
of  the  subject  has  been  fully  discussed  in  many  books, 
while  the  former,  which  are  of  more  interest  to  most 
persons,  have  received  much  less  attention.  The  ques- 
tion of  the  influence  of  forests  on  climate,  which  many 
readers  may  expect  to  find  considered  in  this  book,  is 
omitted  because  it  is  adequately  taken  up  in  Hann's 
Handbook  (Vol.  I). 


vi  PREFACE 

I  have  drawn  very  freely  upon  Hann's  Handbuch 
der  Klimatologie,  Vols.  II  and  III  (2d  ed.,  Stuttgart, 
1897) ,  as  well  as  upon  his  Lehrbuch  der  Meteorologie 
(2d  ed.,  Leipzig,  1906),  two  books  which  are  so  com- 
plete in  all  details  that  every  writer  on  meteorological 
or  climatological  subjects  is  inevitably  very  depend- 
ent upon  them.  The  curves  in  Chapters  IV,  V,  and 
VI  were  all  drawn  from  data  given  in  the  Lehrbuch. 
In  the  chapters  on  the  life  of  man  in  the  different 
zones,  I  have  made  liberal  use  of  Ratzel's  Anthropo- 
geographie  (2d  ed.,  Stuttgart,  1899).  The  princi- 
pal references  other  than  these  are  the  following: 
W.  M.  Davis:  Elementary  Meteorology  (Boston, 
1902)  ;  A.  J.  and  F.  D.  Herbertson:  Man  and  His 
Work  (London,  1899);  W.  Koppen:  Klimakunde. 
I.  Allgemeine  Klimalehre  (2d  ed.,  Leipzig,  1906)  ; 
A.  Supan:  Grundziige  der  pliysischen  Erdkunde  (3d 
ed.,  Leipzig,  1903)  ;  W.  Trabert:  Meteorologie  und 
Klimatologie  (Leipzig  and  Vienna,  1905)  ;  W.  J. 
van  Befcber:  Hygienische  Meteorologie  (Stuttgart, 
1895) ;  A.  Woeikof :  Die  Klimate  der  Erde  (Jena, 
1887) ;  Atlas  of  Meteorology  (Edinburgh,  1899). 

I  am  indebted  to  the  publishers,  Messrs.  G.  P. 
Putnam's  Sons,  for  their  generous  permission  to  me 
to  use  certain  parts  of  this  book  in  an  article  pre- 
pared for  the  Encyclopedia  Britannica  in  1906,  as 
well  as  for  the  privilege  which  they  willingly  accorded 
me  of  publishing  as  separate  articles  many  of  the 
chapters  included  in  this  book.  Chapters  I  to  III 
have  appeared  in  the  Bulletin  of  the  American 


PREFACE  vii 

Geographical  Society;  Chapters  IV  to  VI  in  the 
Journal  of  Geography;  Chapter  VII  in  the  Bulletin 
of  the  Geographical  Society  of  Philadelphia,  and 
Chapter  XI  in  the  Popular  Science  Monthly.  My 
thanks  are  also  due  to  my  fellow-workers,  Professors 
Hann,  Mohn,  Supan,  Koppen,  Angot,  and  W.  M. 
Davis,  and  also  to  Dr.  Fridtjof  Nansen,  for  permis- 
sion to  reproduce  some  of  their  maps  and  diagrams  in 
the  present  volume.  Mr.  Henry  S.  Mackintosh,  of 
Keene,  N.  H.,  has  very  kindly  helped  me  in  the  proof- 
reading. 

ROBERT  DE  C.  WARD. 

Harvard  University, 

Cambridge,  Mass., 
December,  1907. 


NOTE  TO  SECOND  EDITION 

I  have  taken  the  opportunity  offered  'by  the 
publication  of  a  second  edition  of  this  volume  to  make 
some  revision  of  the  chapters  on  The  Characteristics 
of  the  Polar  Zones  and  on  Changes  of  Climate,  in 
order  that  these  subjects  may  be  more  accurately 
presented  in  the  light  of  recent  investigations.  A 
few  other  changes  have  also  been  made,  and  all 
errors  which  occurred  in  the  first  edition  have  been 
corrected. 

ROBERT  DE  C.  WARD. 

August,  1917. 


CONTENTS. 

PAGE 

INTRODUCTION      .        ..'._.        .  .        .        •        1 

Meaning  and  scope  of  climatology — Relation  of 
meteorology  and  climatology — Literature  of  climatol- 
ogy— The  climatic  elements  and  their  treatment — 
Solar  climate — Physical  climate. 

CHAPTER,  I. 

THE  CLIMATIC  ZONES  AND  THEIR  SUBDIVISIONS      .        .         19 

Classification  by  latitude  circles:  the  five  classic 
zones;  Mima  as  used  by  the  Greeks;  Ptolemy's  cli- 
mates; Parmenides;  Polybius;  Posidonius;  Aristotle; 
Eudoxus;  Strabo;  Hippocrates — Temperature  zones: 
Supan  ;  Koppen  ;  Gebelin — Wind  zones  :  Davis; 
Woeikof — Summary  and  conclusions — Necessary 
subdivisions  of  the  zones. 

CHAPTER  II. 

THE  CLASSIFICATION  OF  CLIMATES  ....         35 

Need  of  a  classification  of  climates — Relation  of 
continental  and  ocean  areas  to  temperature:  reasons 
for  the  slow  change  in  the  temperature  of  ocean 
waters — Marine  or  oceanic  climate — Continental  cli- 
mate— Desert  climate — Coast  or  littoral  climate — 
Monsoon  climate — Mountain  and  plateau  climate — 
Mountains  as  climatic  divides. 

CHAPTER  III. 

THE  CLASSIFICATION  OF  CLIMATES  (CONTINUED)      .         .         55 
Supan's   climatic   provinces — Kuppen's   classifica- 

ix 


x  CONTENTS 

PAGE 

tion  of  climates  —  Ravenstein's  hygrothermal  types  — 
Classification  of  rainfall  systems—  Herbertson's  nat- 
ural geographical  regions  —  Summary  and  conclu- 
sions. 

CHAPTER  IV. 

THE  CHARACTERISTICS  OF  THE  ZONES.     I.  THE  TROPICS         76 

General:  climate  and  weather  —  Temperature  —  The 
seasons  —  Physiological  effects  of  heat  and  humidity 
—  Pressure  —  Winds  and  rainfall  —  Land  and  sea 
breezes  —Thunderstorms  —  Cloudiness  —  Intensity  of 
sky-light  and  twilight  —  Climatic  subdivisions:  I. 
The  equatorial  belt  —  II.  Trade  wind  belts  —  III.  Mon- 
soon belts  —  IV.  Mountain  climate. 

CHAPTER  V. 
THE   CHARACTERISTICS   OF  THE   ZONES.     II.  THE  TEM- 

PERATE ZONES     ........       108 

General:   "Temperate"   zones  —  Temperature  — 
Pressure  and  winds  —  Rainfall  —  Humidity  and  cloud- 

— Weather  — 


Climatic  subdivisions  —  South  temperate  zone  —  Sub- 
tropical belts:  Mediterranean  climates  —  North  tem- 
perate zone  :  Western  coasts  —  Interiors  —  Eastern 
coasts  —  Mountain  climates. 

CHAPTER  VI. 

HE  CHARACTERISTICS  OF  THE  ZONES.    III.  THE  POLAR 

ZONES          .........       151 

General  :  relation  to  man,  animals,  and  plants  — 
Temperature:^Pressul'e~^nil~winTjHz::^RaTii  and  snow 
—  Humidity,  cloudiness  and  fog  —  Cyclones  and 
weather  —  Twilight  and  optical  phenomena  —  Physi- 
ological effects. 
—  CHAPTER  VII. 

THE  HYGIENE  OF  THE  ZONES  .....        17s 

Introduction  :  some  general  relations  of  climate  and 
health  —  A  complex   subject  —  Climate,  micro-organ- 


CONTENTS  xi 

PAGE 

isms,  and  disease — Geographical  distribution  of  dis- 
ease— Tropics  :  general  physiological  effects — Trop- 
ical death  rates — Hygiene  in  the  tropics — Tropical 
diseases— Malaria — Yellow  fever — Dysentery:  diar- 
rhceal  disorders — Tropical  abscess  of  the  liver — 
Cholera— Plague — Sunstroke  and  related  conditions 
— Dengue — Beri-beri — Other  minor  diseases — ^Gen- 
eral conclusions :  tropics — Temperate  zones :  gen- 
eral— Winter  and  summer  diseases — Tuberculosis — 
Pneumonia — Diphtheria — Influenza —  Bronchitis — 
Rheumatism — Measles  and  scarlet  fever — Typhoid 
fever — Whooping  cough— Cholera  infantum — Hay 
fever — Polar  zones:  general — Scurvy — Climate  and 
health :  general  conclusion. 

CHAPTER  VIII. 

'HE  LIFE  OF  MAN  IN  THE  TROPICS         .        .  .       220 

_J2Ljmate  and  man:  general — gome  old  views  re- 
garding  the^S'ects  of  climate  on  man- — Factors  in 
^the  problem  other  than  climate — Climate  and  habit- 
ability— The  development  of  the  tropics — The  labour 
problem  in  the  tropics — The  government  of  tropical 
possessions — Primitive  civilisation  and  the  tropics — 
Dwellings  in  the  tropics — Clothing  in  the  tropics — 
Food  in  the  tropics — Agriculture,  arts,  and  industries 
in  the  tropics — Somej)hysioloigical  effects  oftropical 
climates — The  equatorial  forests — The  open  grass- 
lands of  the  tropics:  savannas — Trade  wind  belts  on 
land:  the  deserts — Trade  wind  belts  at  sea — Mon- 
soon districts — Tropical  mountains. 

CHAPTER  IX. 

rHE  LIFE  OF  MAN  IN  THE  TEMPERATE  ZONES         .        .     272 

Climate  and  man  in  the  temperate  zones :  general 
—Northward  movement  of  civilisation  in  the  north 
temperate  zone — Present-day  migrations  within  the 


xii  CONTENTS 

temperate  zones — The  continents  and  the  temperate 
zone — Differences  between  northerners  and  south- 
erners— Variety  of  conditions  in  the  temperate  zones: 
classification — Life  of  man  in  the  forests  of  the  tem- 
perate zone — Forest  clearings — The  steppes — Cli- 
mates and  crops  in  the  temperate  zones — The  deserts 
— Mountains — Climate  and  weather :  some  mental 
effects — Climate  and  weather  and  military  operations 
— Railroads  —  Transportation  by  water — Various 
effects  of  the  weather. 

CHAPTER  X. 

THE  LIFE  OP  MAN  IN  THE  POLAR  ZONES 

General:  a  minimum  of  life — Culture — Subdivisions 
of  the  Arctic  zone~::^Characteristics  of  the  tundra — 
The  reindeer — Population  and  occupations — Dwell- 
ings— Food  and  clothing — Iceland — The  polar  ice 
cap  :  the  Eskimo — Dwellings — Food  and  clothing — 
Travel  and  transportation — Occupations  and  arts — 
Customs — Deserts  of  sand  and  deserts  of  snow. 

CHAPTER  XI. 

CHANGES  OP  CLIMATE 

Popular  belief  in  climatic  change — Evidence  of 
climatic  changes  within  historic  times — What  mete- 
orological records  show — Why  the  popular  belief  in 
climatic  changes  is  untrustworthy — Value  of  evi- 
dence concerning  changes  of  climate — Periodic  oscil- 
lations of  climate:  the  sunspot  period — Bruckner's 
35-year  cycle — Climatic  cycles  of  longer  period — 
Geological  changes  in  climate — Conclusion. 

INDEX 


ILLUSTRATIONS. 

VI G.  PAGB 

1  DISTRIBUTION  OF  INSOLATION  OVER  THE  EABTH      .  8 

2  ANNUAL  VARIATION  OP  INSOLATION  AT  DIFFERENT 

LATITUDES 10 

3  INSOLATION    RECEIVED   AT  DIFFERENT    LATITUDES 

ON  JUNE  21 14 

4  THE  ZONES  IN  THE  TIME  OF  PARMENIDES       .        .  22 

5  SUPAN'S  TEMPERATURE  ZONES           ....  25 

6  TEMPERATURE  ZONES  AFTER  KOPPEN       ...  27 

7  INFLUENCE  OF  LAND  AND  WATER  ON  THE  ANNUAL 

MARCH  OF  AIR  TEMPERATURE      ....  39 

8  DIURNAL  VARIATION    OF  PRESSURE:  INFLUENCE  OF 

ALTITUDE 48 

9  DIURNAL  VARIATION  OF  TEMPERATURE:  INFLUENCE 

OF  ALTITUDE 50 

10  SUPAN'S  CLIMATIC  PROVINCES 56 

11  GENERAL  DISTRIBUTION  OF  PLANT  ZONES       .        .  63 

12  SCHEME  OF  CLIMATES  AT  SEA-LEVEL        ...  64 

13  NAMES  OF  CLIMATES  AT  SEA-LEVEL          ...  65 

14  VERTICAL  DISTRIBUTION  OF  CLIMATES      ...  66 

15  PRESSURE  AND  WINDS  IN  JANUARY          .         .  67 

16  PRESSURE  AND  WINDS  IN  JULY        ....  68 

17  KOPPEN'S    CLASSIFICATION  OF  CLIMATES   IN   RELA- 

TION TO  VEGETATION  69 


xiv  ILL  USTRA  TIONS 

FIG.  PAGE 

18  HERBERTSON'S  MAJOR  NATURAL  REGIONS        .         .  71 

19  ANNUAL    MARCH    OF    TEMPERATURE:    EQUATORIAL 

TYPE 91 

20  ANNUAL  MARCH  OP  RAINFALL  IN  THE  TROPICS      .  92 

21  ANNUAL  MARCH  OF  CLOUDINESS  IN  THE  TROPICS   .  95 

22  ANNUAL  MARCH  OF  TEMPERATURE:  TROPICAL  TYPE  97 

23  MONTHLY   DISTRIBUTION  OF  RAINFALL:  SUB-TROPI- 

CAL WINTER  RAINS 125 

24  RAINY  AND  RAINLESS  ZONES   ON  EASTERN  ATLAN- 

TIC COAST 128 

25  ANNUAL  MARCH   OF   TEMPERATURE  FOR   SELECTED 

SUB-TROPICAL  STATIONS         .  131 

26  ANNUAL   MARCH  OF  CLOUDINESS   IN  A  SUB-TROPI- 

CAL CLIMATE 133 

27  ANNUAL   MARCH   OF   TEMPERATURE  FOR  SELECTED 

STATIONS  IN  THE  TEMPERATE  ZONES   .         .         .  135 

28  ANNUAL  MARCH  OF  RAINFALL  :   TEMPERATE  ZONES  139 

29  ANNUAL  MARCH   OF   CLOUDINESS   IN  CONTINENTAL 

AND  MOUNTAIN  CLIMATES:  TEMPERATE  ZONES     .  147 

30  JANUARY  NORTH  POLAR  ISOTHERMS          .         .         .  155 

31  JULY  NORTH  POLAR  ISOTHERMS        .         .         .         .156 

32  MEAN  ANNUAL  NORTH  POLAR  ISOTHERMS        .         .  158 

33  ANNUAL  MARCH  OF  TEMPERATURE:  POLAR  TYPE   .  164 

34  ANNUAL    MARCH    OF    CLOUDINESS    IN  THE  NORTH 

POLAR  ZONE:  MARINE  TYPE  173 


ACKNOWLEDGMENT  OF  ILLUSTRATIONS. 

Fig.  1.    W.  M.  Davis:  Elementary  Meteorology. 
"    2,  3,  7,  8,  9.    A.  Angot:  Traite  elementaire  de  Meteorologie. 

'*  4.  H.  Berger:  Geschichte  der  wissenschaftlichen  Erdkunde  der 
Griechen. 

"  5, 10,  24.  A.  Supan :  Ghrundzuge  der  physischen  Erdkunde.  3d 
edition. 

"  6.  W.  Koppen :  Die  Warmezonen  der  Erde,  nach  der  Dauer  der 
heifisen,  gemdssigten  und  kalten  Jahreszeit,  und  nach  der 
Wirkung  der  Warme  auf  die  organische  Welt  betrachtet. 
Met.  Zeitschr.,  i,  1884. 

"  11, 12, 13, 14, 15,  16, 17.  W.  Koppen  :  Versuch  einer  Klassifikation 
der  Klimate,  vorzugsweise  nach  ihren  Beziehungen  zur 
Pflanzenwelt.  Hettner's  Geogr.  Zeitschr.,  vi,  1900. 

"  18.  A.  J.  Herbertson  :  The  Major  Natural  Regions.  Geogr.  Jour. , 
xxv,  1905. 

"  30,  31,  32.  Scientific  Results  of  the  Norwegian  North  Polar  Expedi- 
tion. Vol.  vi,  Meteorology. 


rv 


CLIMATE 


INTRODUCTION 


Meaning  and  Scope  of  Climatology  —  Relation  of  Meteorology  and 
Climatology  —  Literature  of  Climatology  —  The  Climatic  Ele- 
ments and  their  Treatment  —  Solar  Climate  —  Physical  Climate. 


Meaning  and  Scope  of  Climatology.  The  word 
Mima  (from  uhivsir,  to  incline),  as  used  by  the 
Greeks,  originally  referred  to  the  supposed  slope  of 
the  earth  toward  the  pole,  or  to  the  inclination  of  the 
earth's  axis  or  of  the  sun's  rays.  It  may,  perhaps, 
have  had  reference  to  the  different  exposures  of 
mountain  slopes.  Later,  probably  after  Aristotle's 
time,  it  came  to  be  used  as  about  equivalent  to  our 
zone,  but  at  first  it  was  simply  a  mathematical  or  an 
astronomical  term,  not  associated  with  any  idea  of 
physical  climate.  A  change  of  latitude  in  those  days 
meant  a  change  of  climate.  Such  a  change  was 
gradually  seen  to  mean  a  change  of  atmospheric  con- 
ditions as  well  as  a  change  in  length  of  day.  Thus 
Mima  came  to  have  its  present  meaning. 

An  excellent  illustration  of  the  ancient  meaning  of 


INTRODUCTION 

the  word  Mima  is  found  in  the  system  of  climates  pro- 
posed by  the  famous  geographer,  Ptolemy.  This 
was  a  division  of  the  earth's  surface  between  equator 
and  north  pole  into  a  series  of  climates,  or  parallel 
zones,  separated  by  latitude  circles  and  differing  from 
one  another  simply  in  the  length  of  their  longest  day. 
Ptolemy's  subdivision  of  the  earth's  surface  was  really 
nothing  but  an  astronomical  climatic  table. 

Climate,  as  we  use  the  term,  is  the  resultant  of  the 
average  atmospheric  conditions,  or,  more  simply,  it 
is  the  average  condition  of  the  atmosphere.  Weather 
is  a  single  occurrence,  or  event,  in  the  series  of  condi- 
tions which  make  up  the  climate.  The  climate  of  a 
place  is  in  a  sense  its  average  weather.  The  average 
values  of  these  atmospheric  conditions  can  be  deter- 
mined only  by  means  of  careful  observations,  con- 
tinued for  a  period  sufficiently  long  to  give  accurate 
results.  Climatology  is  the  study  or  science  of 
climates. 

Relation  of  Meteorology  and  Climatology.  Mete- 
orology and  climatology  are  interdependent.  It  is 
impossible  to  distinguish  very  sharply  between  them. 
Each  needs  the  results  obtained  by  the  other.  In  a 
strict  sense,  meteorology  deals  with  the  physics  of 
the  atmosphere.  It  considers  the  various  atmo- 
spheric phenomena  individually,  and  seeks  to  deter- 
mine their  physical  causes  and  relations.  Its  view  is 
largely  theoretical.  The  aspect  of  meteorology  which 
is  of  most  immediate  practical  importance  to  man  is 
that  which  concerns  weather- forecasting. 


INTRODUCTION  3 

When  the  term  meteorology  is  used  in  its  broadest 
meaning,  climatology  is  a  subdivision  of  meteorology. 
Climatology  is  largely  descriptive.  It  aims  to  give 
as  clear  a  picture  as  possible  of  the  interaction  of  the 
various  atmospheric  phenomena  at  any  place  on  the 
earth's  surface.  It  rests  upon  physics  and  geogra- 
phy, the  latter  being  a  very  prominent  factor.  Cli- 
matology may  almost  be  defined  as  geographical 
meteorology.  Its  main  object  is  to  be  of  practical 
service  to  man.  Its  method  of  treatment  lays  most 
emphasis  on  the  elements  which  are  of  the  most  im- 
portance to  life.  Climate  and  crops,  climate  and 
industry,  climate  and  health,  are  subjects  of  vital 
interest  to  man.  No  other  science  concerns  man  more 
closely  in  his  daily  life. 

Literature  of  Climatology.  Scientific  climatology 
is  based  upon  numerical  results  obtained  by  system- 
atic, long-continued,  and  accurate  meteorological 
observations.  The  essential  part  of  its  literature  is 
therefore  found  in  the  collections  of  data  published 
by  the  various  meteorological  services  and  observator- 
ies. In  addition,  large  numbers  of  short  sketches  and 
notes  on  climate,  partly  the  more  or  less  haphazard 
accounts  of  travellers,  partly  the  more  careful  studies 
of  scientific  observers,  are  scattered  through  a  wide 
range  of  geographical  and  other  publications.  The 
only  comprehensive  text-book  of  climatology  is  the 
Handbuch  der  Klimatologie  of  Professor  Julius 
Hann,  of  the  University  of  Vienna.  This  is  the 
standard  book  on  the  subject,  and  upon  it  is  based 


4  INTRODUCTION 

much  of  the  present  volume,  and  of  other  recent 
discussions  of  climate.  The  second  edition  of  this 
work,  in  three  volumes,  was  published  in  1897  (Stutt- 
gart, Engelhorn) .  The  first  volume  deals  with  gen- 
eral climatology,  and  has  been  translated  into 
English.1  The  second  and  third  volumes  are  de- 
voted to  the  climates  of  the  different  countries  of  the 
world.  Woeikofs  Die  Klimate  der  Erde  (Jena, 
Costenoble,  1887)  is  also  a  valuable  reference  book. 
The  first  part  concerns  general  relations  of  climate, 
particularly  to  rivers  and  lakes,  to  vegetation,  and  to 
snow-cover,  while  the  second  part  deals  with  the 
climates  of  special  areas.  The  standard  meteorologi- 
cal journal  of  the  world,  the  Meteor 'ologische  Zeit- 
schrift  (Braunschweig,  Vieweg,  monthly),  is  indis- 
pensable to  anyone  who  wishes  to  keep  in  touch  with 
the  latest  publications  on  climatology,  for  it  contains 
the  most  complete  record  of  such  literature,  as  well 
as  a  large  number  of  original  notes  and  discussions. 
The  newest  and  most  complete  collection  of  charts  is 
that  in  the  Atlas  of  Meteorology  (London,  Con- 
stable, 1899),  in  which  also  there  is  an  excellent 
bibliography.  For  the  titles  of  more  recent  pub- 
lications reference  may  be  made  to  the  Interna- 
tional Catalogue  of  Scientific  Literature  (annual 
volume  on  Meteorology) ;  or  to  the  more  frequent 
bibliographical  lists  in  the  Meteorologische  Zeit- 
schrift;  the  Monthly  Weather  Review  (Washington, 
U.  S.  Weather  Bureau)  ;  the  Quarterly  Journal  of 
*By  R.  De  C.  Ward.  London  and  New  York,  Macmillan,  1903. 


INTRODUCTION  5 

the  Royal  Meteorological  Society  (London),  and  the 
Halbmonatliches  Litteraturverzeichniss  der  ff  Fort- 
schritte  der  Physik"  (Braunschweig,  Vieweg,  twice 
a  month) . 

The  Climatic  Elements  and  their  Treatment. 
Climatology  has  to  deal  with  the  same  groups  of  at- 
mospheric conditions  as  those  with  which  meteorology 
is  concerned,  viz.:  temperature  (including  radiation) ; 
moisture  (including  humidity,  precipitation,  and 
cloudiness) ;  wind  (including  storms)  ;  pressure; 
evaporation,  and  also,  but  of  less  importance,  the 
composition  and  the  chemical,  optical,  and  electrical 
phenomena  of  the  atmosphere.  The  characteristics 
of  each  of  these  so-called  climatic  elements  are  set 
forth  in  a  standard  series  of  numerical  values,  based 
on  careful,  systematic,  and  long-continued  meteoro- 
logical records,  corrected  and  compared  by  well- 
known  methods.  Various  forms  of  graphic  presen- 
tation, by  curves,  or  by  wind  roses,  etc.,  are  employed 
to  emphasise  and  simplify  the  numerical  results. 
Instructions  concerning  the  use,  exposure,  hours  of 
observation,  and  corrections  of  the  ordinary  meteoro- 
logical instruments;  as  well  as  for  obtaining  the 
usual  numerical  results,  are  published  by  the  various 
governmental  meteorological  services.  In  Hann's 
Handbook  of  Climatology,  Vol.  I,  will  be  found  a 
general  discussion  of  the  methods  of  presenting  the 
different  climatic  elements,  and  of  the  reasons  for 
adopting  the  accepted  scheme  of  presentation.  The 
most  complete  guide  in  the  numerical,  mathematical, 


6  INTRODUCTION 

and  graphic  treatment  of  meteorological  data  for 
climatological  purposes  is  Hugo  Meyer's  Anleitung 
zur  Bearbeitung  meteorologischer  Beobachtungen 
filr  die  Klimatologie  (Berlin,  Springer,  1891). 

Climate  deals  first  of  all  with  average  conditions, 
as  is  apparent  from  the  definition  given  above.  But 
means  may  be  made  up  of  very  different  values  of  the 
elements  which  go  into  them,  and  therefore  a  satis- 
factory presentation  of  a  climate  must  include  more 
than  mere  averages.  It  must  take  account,  also,  of 
regular  and  irregular  daily,  monthly,  and  annual 
changes,  and  of  the  departures,  mean  and  extreme, 
from  the  average  conditions  which  may  occur  at  the 
same  place  in  the  course  of  time.  The  mean  mini- 
mum and  the  mean  maximum  temperature  or  rainfall 
of  a  month,  or  a  season,  are  important  data,  not  in  any 
way  replaced  by  a  knowledge  of  the  mean  monthly 
or  seasonal  temperature  and  rainfall.  Further,  a 
determination  of  the  frequency  of  occurrence  of  a 
given  condition,  or  of  certain  values  of  that  condition, 
is  important,  for  periods  of  a  day,  month,  or  year,  as, 
for  example,  the  frequency  of  winds  according  to  < 
direction  or  velocity;  or  of  different  amounts  of 
cloudiness;  or  of  temperature  changes  of  5,  or  10, 
or  more  degrees;  the  number  of  days  with  and  with- 
out rain  or  snow  in  any  month,  or  year,  or  with  rain 
of  a  certain  amount,  etc.  The  probability  of  occur- 
rence of  any  condition,  as  of  rain  in  a  certain  month; 
or  of  a  temperature  of  32°,  for  example,  is  also  a 
useful  thing  to  know  concerning  a  climate.  In  the 


INTRODUCTION  7 

past,  climatology  has  been  too  much  concerned  with 
monthly,  seasonal,  and  annual  averages.  An  im- 
portant addition  to  the  usual  climatic  summaries 
would  be  the  introduction,  for  all  regions  in  which  the 
cyclonic  or  storm  control  of  weather  conditions  is 
characteristic,  of  the  cyclonic  unit,  so  that,  for  ex- 
ample, the  average  duration  and  value  of  cyclonic 
ranges  of  temperature  in  the  several  months,  or  the 
proportion  of  the  annual  rain  and  snowfall  received 
from  cyclonic  storms  and  from  local  thunderstorms, 
might  be  determined.1 

Solar  Climate.  The  sun  is  clearly  the  principal 
control  of  climates  on  the  earth's  surface.  The  gen- 
eral distribution  of  temperature,  as  well  as  the  sea- 
sonal and  diurnal  changes,  all  depend  upon  changes 
in  the  intensity  of  sunshine.  Hence  a  brief  considera- 
tion of  the  distribution  of  insolation  over  the  earth's 
surface  is  essential  to  a  proper  understanding  of  cli- 
mates. Climate,  in  so  far  as  it  is  controlled  solely  by 
the  amount  of  solar  radiation  which  any  place  receives 
by  reason  of  its  latitude,  is  called  solar  climate. 
Clearly,  all  places  on  the  same  latitude  circle  would 
have  the  same  solar  climate,  for  the  intensity  and 
amount  of  insolation  depend  upon  the  angle  of  in- 
cidence of  the  sun's  rays,  and  upon  the  length  of  day, 
and  both  of  these  depend  upon  latitude.  Solar  cli- 
mate alone  would  prevail  if  the  earth  had  a  homo- 

1  See  R.  DeC.  Ward :  Suggestions  Concerning  a  More  Rational 
Treatment  of  Climatology.  Report  Eighth  International  Geo- 
graphic Congress,  Washington,  D.  C.,  1904,  pp.  277-293. 


8 


INTRODUCTION 


geneous  land  surface,  and  if  there  were  no 
atmosphere.  For  under  these  conditions,  and  with- 
out air  or  ocean  currents,  the  distribution  of  tem- 
perature at  any  place  would  depend  solely  on  the 
amount  of  energy  received  from  the  sun,  and  upon 
the  loss  of  heat  by  radiation.  And  these  two  factors 
would  have  the  same  value  at  all  points  on  the  same 
latitude  circle. 

The  relative  amounts  of  insolation  received  at  dif- 
ferent latitudes  and  at  different  times  have  been  care- 
fully determined.  The  values  all  refer  to  conditions 
at  the  upper  limit  of  the  earth's  atmosphere,  i.  e., 


FIG.  i.    DISTRIBUTION  OF  INSOLATION  OVER  THE  EARTH 

without  the  effect  of  absorption  by  the  atmosphere. 
The  accompanying  diagram  (see  Fig.  I)  shows  very 
clearly  the  distribution  of  insolation  in  both  hemi- 


INTRODUCTION  9 

spheres  at  different  latitudes  and  at  different  times  in 
the  year.  The  latitudes  are  given  at  the  left  margin 
and  the  time  of  year  at  the  right  margin.  The  values 
of  insolation  are  shown  by  the  vertical  distance  above 
the  plane  of  the  two  margins. 

At  the  equator,  where  the  day  is  always  twelve 
hours  long,  there  are  two  maxima  of  insolation  at  the 
equinoxes,  when  the  sun  is  vertical  at  noon,  and  two 
minima  at  the  solstices,  when  the  sun  is  farthest  off 
the  equator.  The  annual  curves  show  that  the  valuer 
do  not  vary  much  through  the  year,  because  the  sun 
is  never  very  far  from  the  zenith,  and  day  and  night 
are  always  equal.  There  is  a  slight  difference  in  the 
insolation  at  the  two  maxima,  owing  to  a  difference 
in  the  sun's  distance,  the  earth's  orbit  being  an  ellipse 
and  not  a  circle.  The  earth  is  nearer  the  sun  in  the 
winter  of  the  northern  hemisphere,  and  therefore  the 
spring  maximum  is  somewhat  greater  than  the  au- 
tumn maximum.  The  varying  distance  from  the  sun 
also  explains  the  fact  that  the  maxima  of  insolation 
do  not  come  exactly  on  the  dates  of  the  equinoxes. 

These  conditions  are  clearly  brought  out  in  curve 
1  of  Fig.  2,  which  shows  the  annual  march  of  insola- 
tion on  the  equator.  The  law  of  the  distribution  of 
insolation  would  be  simple  if  the  sun  were  always  on 
the  equator,  for  the  angle  of  insolation  and  the  length 
of  day  and  night  would  then  always  remain  the  same. 
But  under  existing  conditions,  both  the  angle  of  in- 
solation and  the  length  of  day  are  constantly  chang- 
ing, and  the  interaction  between  these  two  controls 


10 


INTRODUCTION 


becomes  very  complex.  As  the  latitude  increases,  the 
angle  of  insolation  becomes  more  oblique,  and  the 
intensity  of  insolation  decreases,  but  at  the  same  time 
the  length  of  day  rapidly  increases  during  the  sum- 
mer, and  towards  the  pole  of  the  hemisphere  which  is 
having  its  summer  the  gain  in  insolation  from  the 


Jan.  Feb.  Mar.  Apr.  May  June  July  Aug.  Sept.  Oct.  Nov.  Dec.  Jan. 


Jan.  Feb.  Mar.  Apr.  May  June  July  Aug.  Sept.  Oct.  Nov.  Dec.  Jan., 
FIG.  2.    ANNUAL  VARIATION  OF  INSOLATION  AT  DIFFERENT  LATITUDES 

latter  cause  more  than  compensates  for  the  loss  by 
the  former.  The  double  period  of  insolation,  above 
noted  for  the  equator^  prevails  as  far  as  about  lat.  12° 
N.  and  S.;  at  lat.  15°  the  two  maxima  have  united, 


INTRODUCTION  11 

and  the  same  is  true  of  the  minima.  Take  the 
case  of  an  intermediate  latitude,  like  45°  N.  (see 
curve  2,  Fig.  2).  Here  there  is  one  minimum,  in 
December,  when  the  sun  is  south  of  the  equator,  and 
one  maximum,  in  June,  when  the  sun  is  north.  The 
slight  displacement  of  this  maximum  and  minimum 
from  the  exact  jiate  of  the  two  solstices  is  due  to  the 
difference  in  the  sun's  distance.  At  the  north  pole 
(curve  3,  Fig.  2),  there  is  one  maximum  at  the 
summer  solstice,  and  no  insolation  at  all  while  the  sun 
is  below  the  horizon.  The  distribution  of  insolation 
at  different  latitudes  on  the  same  day  is  also  interest- 
ing. On  June  21,  for  example  (see  Fig.  1),  the 
equator  has  a  day  twelve  hours  long,  but  the  sun's 
maximum  altitude  is  only  66^°,  i.  e.,  it  does  not 
reach  the  zenith,  and  the  amount  of  insolation 
is  less  than  at  the  equinox.  On  the  northern 
tropic,  however,  the  sun  is  vertical  at  noon,  and  the 
day  is  between  thirteen  and  fourteen  hours  long. 
Hence  the  amount  of  insolation  received  at  this  lati- 
tude on  June  21  is  greater  than  that  received  on  the 
equinox  at  the  equator.  As  one  passes  from  the 
tropic  to  the  pole  the  sun  stands  lower  and  lower 
at  noon,  and  the  value  of  insolation  would 
steadily  decrease  with  latitude  if  it  were  not 
for  the  increase  in  the  length  of  day.  Going  pole- 
wards from  the  northern  tropic  on  June  21,  the 
value  of  insolation  increases  for  a  time,  because,  al- 
though the  sun  is  lower,  the  number  of  hours  during 
which  it  shines  is  greater.  A  maximum  value  is 


12  INTRODUCTION 

reached  at  about  lat.  43^°  N.  The  decreasing  alti- 
tude of  the  sun  then  more  than  compensates  for  the 
increasing  length  of  day,  and  the  value  of  insolation 
diminishes,  a  minimum  being  reached  at  about  lat. 
62°.  Then  the  rapidly  increasing  length  of  day  to- 
wards the  pole  (the  day  being  twenty-four  hours  long 
beyond  the  Arctic  circle)  again  brings  about  an  in- 
crease in  the  value  of  insolation,  until  a  maximum  is 
reached  at  the  pole  which  is  greater  than  the  value  re- 
ceived at  the  equator  at  any  time.  (See  Fig.  2,  in 
which  the  curves  are  all  drawn  on  the  same  scale). 
The  length  of  day  is  the  same  on  the  Arctic  circle 
as  at  the  pole  itself,  but  while  the  altitude  of  the  sun 
varies  during  the  day  on  the  former,  being  at  the  hori- 
zon at  midnight  and  highest  at  noon,  the  altitude  at 
the  pole  remains  231/2°  throughout  the  twenty-four 
hours.  The  result  is  to  give  the  pole  a  maximum 
(See  Fig.  3,  curve  marked  1.00.) .  On  June  21,  there 
are  therefore  two  maxima  of  insolation,  one  at  lat. 
431/2  °  and  one  at  the  north  pole.  From  lat.  431/0° 
N.,  insolation  decreases  to  zero  on  the  Antarctic 
circle,  for  sunshine  falls  more  and  more  obliquely, 
and  the  day  becomes  shorter  and  shorter.  Beyond 
lat.  66%°  S.  the  night  lasts  twenty-four  houis.  On 
December  21  (see  Fig.  1),  the  conditions  in  southern 
latitudes  are  similar  to  those  in  the  northern  hemi- 
sphere on  June  21,  but  the  southern  latitudes  have 
higher  values  of  insolation  because  the  earth  is  then 
nearer  the  sun. 

At  the  equinox,  the  days  are  equal  everywhere,  but 


INTRODUCTION  13 

the  noon  sun  is  lower  and  lower  with  increasing  lati- 
tude in  both  hemispheres  until  the  rays  are  tangent  to 
the  earth's  surface  at  the  poles  (except  for  the  effect 
of  refraction).  Therefore,  the  values  of  insolation 
diminish  from  a  maximum  at  the  equator  to  a  mini- 
mum at  both  poles.  From  the  fact  that  the  southern 
hemisphere  has  its  summer  in  perihelion  and  its  win- 
ter in  aphelion,  it  follows  that  there  is  a  greater  dif- 
ference between  the  seasonal  values  of  insolation  south 
of  the  equator  than  north  of  it.  In  other  words,  the 
solar  climate  of  the  southern  hemisphere  is  more  se- 
vere than  that  of  the  northern.  Nevertheless,  owing 
to  the  fact  that  the  earth  moves  more  rapidly  around 
its  orbit  when  nearest  the  sun,  both  hemispheres  re- 
ceive equal  amounts  of  insolation  at  the  same  lati- 
tudes, and  in  the  mean  of  the  year,  both  have  the  same 
amount  of  insolation. 

The  values  of  insolation  thus  far  considered  have 
reference  to  the  upper  limit  of  the  earth's  atmosphere, 
or  to  the  earth's  surface  assuming  that  no  atmosphere 
exists.  The  effect  of  the  atmosphere  is  to  weaken  the 
sun's  rays.  The  more  nearly  vertical  the  sun,  the  less 
the  thickness  of  atmosphere  traversed  by  the  rays. 
The  values  of  insolation  at  the  earth's  surface,  after 
passage  through  the  atmosphere,  have  been  calcu- 
lated. They  vary  much  with  the  condition  of  the  air, 
as  to  dust,  clouds,  water  vapour,  etc.  In  Fig.  2,  the 
broken  lines,  4,  5,  and  6,  show  the  values  of  insolation 
at  the  equator,  lat.  45°  1ST.,  and  the  north  pole,  allow- 
ing for  a  loss  of  25  %  during  the  passage  through  the 


14 


INTRODUCTION 


atmosphere,  i.  e.,  with  a  coefficient  of  transmission 
0.75.  This  is  higher  than  that  usually  observed,  even 
under  very  favourable  conditions,  with  the  ^un  in  the 
zenith.  As  a  rule,  even  when  the  sky  is  clear,  about 
one-half  of  the  solar  radiation  is  lost  during  the  day 


0.50 


Pole  80°    60°     40°    20°      0*      20°     40°     60°    80°Po!e 
South  North 

FIG.  3.    INSOLATION  RECEIVED  AT  DIFFERENT  LATITUDES  ON  JUNE  21 

by  atmospheric  absorption.  The  great  weakening  of 
insolation  at  the  pole,  where  the  sun  is  very  low,  is 
especially  noticeable.  The  effect  of  the  atmosphere 
is  also  shown  in  Fig.  3.  The  upper  curve  represents 


INTRODUCTION 


15 


the  total  quantity  of  insolation  received  at  the  earth's 
surface  with  a  coefficient  of  transmission  of  1.00 
(i.  e.,  no  loss).  Under  such  conditions,  as  already 
noted,  there  are  two  maxima  on  June  21,  at  lat.  431/2° 
N.  and  at  the  north  pole.  The  second  curve  cor- 
responds to  a  coefficient  of  transmission  of  0.75,  which 
is  also  used  in  the  broken  curves  of  Fig.  2.  Under 
these  conditions,  there  is  but  one  maximum,  at  about 
lat.  36°  N.,  and  the  north  pole  has  only  49%  of  the 
total  radiation  emitted  by  the  sun.  The  third  curve 
is  based  on  a  coefficient  of  transmission  of  0.50,  and 
shows  one  maximum  at  lat.  32°  N.,  the  pole  receiving 
only  18%  of  the  total  amount  which  reaches  the  upper 
limit  of  the  atmosphere  at  that  point.  The  curves 
0.75  and  0.50  show  that,  taking  the  atmosphere  into 
account,  even  in  midsummer  the  amount  of  insolation 
decreases  from  between  lats.  30°  and  40°  to  the  pole. 
The  following  table  (after  Angot)  shows  the  effect 
of  the  earth's  atmosphere  (coefficient  of  transmis- 
sion 0.7)  upon  the  value  of  insolation  received  at  sea 
level. 

VALUES    OF    DAILY    INSOLATION    AT    THE    UPPER    LIMIT    OF    THE 

EARTH'S  ATMOSPHERE  AND  AT  SEA  LEVEL. 


Lat. 

Upper  limit  of  atmosphere 

Earth's  surface 

Equator 

40° 

N.  Pole 

Equator 

40° 

N.  Pole 

Winter  Solstice    . 
Equinoxes  . 
Summer  Solstice  . 

948 
1000 
888 

360 
773 
1115 

0 
0 
1210 

552 
612 
517 

124 
411 
660 

0 
0 
494 

16  INTRODUCTION 

The  following  table  gives,  according  to  Zenker, 
the  relative  thickness  of  the  atmosphere  at  different 
altitudes  of  the  sun,  and  also  the  amount  of  trans- 
mitted insolation. 

RELATIVE   DISTANCES   TRAVERSED   BY    SOLAR  RAYS    THROUGH   THE 
ATMOSPHERE,  AND   INTENSITIES  OF   RADIATION   PER   UNIT   AREAS 

Altitude  of  Sun. 
o°  |    5°  I    10°  |  20°  |  30°  I  40°  I  50°  I  60°  I   70°  I  80°  I   90° 

Relative  Lengths  of  Path  through  the  Atmosphere. 
44.7!  IO-8  |  5-7   |  2.92  |  2.00  |  1.56  |  1.31"!  1.15  |  i. 06  |  1.02  I  i. oo 

Intensity  of  Radiation  on  a  Surface  Normal  to  the  Rays. 
o.o  I  0.15  I  0.31  I  0.51  I  0.62  I  0.68  |  0.72  |  0.75  |  0.76  |  0.77  |  0.78 

Intensity  of  Radiation  on  a  Horizontal  Surface, 
o.o  |  o.oi  I  0.05  I  0.17  I  0.31  I  0.44  I  0.55  I  0.65  I  0.72  i  0.76  I  0.78 

Physical  Climate.  It  is  clear  that  the  distribution  of 
insolation,  just  considered,  explains  many  of  the  large 
facts  of  the  distribution  of  temperature — for  example, 
the  decrease  of  temperature  from  equator  to  poles; 
the  double  maximum  of  temperature  on  and  near  the 
equator;  the  increasing  seasonal  contrasts  with  in- 
creasing latitude,  etc.  But  it  is  equally  apparent  that 
the  distribution  of  temperature  often  does  not  follow 
the  distribution  of  insolation  closely,  for,  if  it  did 
so,  the  two  poles  would  be  warm  at  the  times  of  their 
respective  maxima  of  insolation.  The  high  values  of 
insolation  at  the  poles  do  not  correspond  to  high  tem- 
peratures, as  will  be  seen  in  a  later  chapter  (VI). 


INTRODUCTION  17 

The  old  view  which  thus  explained  an  "  open  polar 
sea"  was  erroneous.  The  distribution  of  insolation 
suggests  a  subdivision  of  the  earth's  surface  into 
three  distinct  belts.  In  one,  within  about  12°  of  the 
equator,  there  are  two  maxima  and  two  minima.  In 
a  second,  there  is  one  maximum;  and  for  part  of  the 
year  the  absence  of  the  sun  reduces  the  amount  to 
zero.  In  a  third,  the  conditions  are  intermediate; 
there  is  one  maximum  and  one  minimum,  but  there  is 
no  time  when  the  value  of  insolation  decreases  to 
zero.  Of  the  second  and  third  of  these  belts,  there  are 
two  divisions,  one  in  the  northern  and  one  in  the 
southern  hemisphere.  It  will  be  noted  that  the 
tropics,  the  polar,  and  the  temperate  zones  roughly 
correspond  to  these  insolation  belts. 

The  regular  distribution  of  solar  climate  between 
equator  and  poles  which  would  exist  on  a  homogene- 
ous earth,  whereby  similar  conditions  prevail  along 
each  latitude  circle,  is  very  much  modified  by  the  un- 
equal distribution  of  land  and  water;  by  differences 
of  altitude;  by  air  and  ocean  currents;  by  varying 
conditions  of  cloudiness,  and  so  on.  Hence  the  cli- 
mates met  with  along  the  same  latitude  circle  are  no 
longer  all  alike.  Solar  climate  is  greatly  modified  by 
atmospheric  conditions  and  by  the  surface  features  of 
the  earth,  and  what  is  known  as  physical  climate  is 
the  result.  The  uniform  latitudinal  arrangement  of 
solar  climatic  belts  is  interfered  with.  Physical  cli- 
mate results  from  the  reaction  of  the  earth's  surface 
features  upon  the  atmosphere.  According  to  the 


18  INTRODUCTION 

dominant  control,  in  each  case,  we  have  solar,  conti- 
nental, marine,  and  mountain  climates.  In  the  first 
named,  latitude  is  the  essential;  in  the  second  and 
third,  the  effect  of  land  or  water;  in  the  fourth,  the 
effect  of  altitude. 


CHAPTER  I 

THE  CLIMATIC  ZONES  AND  THEIR  SUBDIVISIONS 

Classification  by  Latitude  Circles:  The  Five  Classic  Zones;  Klima 
as  Used  by  the  Greeks;  Ptolemy's  Climates;  Parmenides; 
Polybius;  Posidonius;  Aristotle;  Eudoxus;  Strabo;  Hippoc- 
rates— Temperature  Zones:  Supan;  Koppen;  Gebelin — Wind 
Zones:  Davis;  Woeikof — Summary  and  Conclusions — Neces- 
sary Subdivisions  of  the  Zones. 

Classification  by  Latitude  Circles.  So  great  is  the 
variety  of  climates  to  be  found  in  different  parts  of 
the  world  that  it  has  long  been  customary  to  classify 
these  climates  roughly  into  certain  broad  belts. 
These  are  the  climatic  zones.  A  simple  grouping  of 
this  kind  can,  however,  obviously  take  account  only 
of  the  most  general  characteristics  of  the  climates  , 
which  are  included  within  each  zone.  The  five  zones 
with  which  we  are  most  familiar  are  the  so-called  tor- 
rid, the  two  temperate,  and  the  two  frigid  zones.  The 
torrid,  or,  better,  the  tropical  zone,  naming  it  by  its 
boundaries,  is  limited  on  the  north  and  south  by  the 
two  tropics  of  Cancer  and  Capricorn,  the  equator 
dividing  the  zone  into  two  equal  parts.  The  temper- 
ate zones  are  limited  towards  the  equator  by  the 
tropics,  and  towards  the  poles  by  the  Arctic  and  Ant- 
arctic circles.  The  two  frigid,  or,  better,  the  two  polar 

19 


20  CLIMATE 

zones,  are  caps  covering  both  polar  regions,  and 
bounded  on  the  side  towards  the  equator  by  the  Arctic 
and  Antarctic  circles. 

These  five  zones  are  classified  on  purely  astronomi- 
cal or  mathematical  grounds.  They  are  really  zones 
of  sunshine,  or  of  solar  climate.  Within  the  tropical 
zone,  the  sun  reaches  the  zenith  at  two  different  times 
in  the  year;  its  greatest  possible  zenith  distance  is 
47° ;  the  day  is  never  less  than  ten  and  a  half  hours 
long.  On  the  tropics  themselves,  the  sun  reaches  the 
zenith  but  once  a  year.  In  the  polar  zones,  the  sun  is 
below  the  horizon  for  twenty-four  hours  at  least  once 
in  winter,  and  is  above  the  horizon  for  the  same  length 
of  time  at  least  once  in  summer.  On  the  polar  circles, 
the  noon  altitude  of  the  sun  decreases  to  0°  on  the 
shortest  day.  The  temperate  zone  has  conditions  be- 
tween these  two  extremes.  At  no  point  can  the  sun 
be  in  the  zenith;  nor,  except  on  the  polar  circles,  is 
there  ever  anywhere  a  twenty-four-hour  day  or  night. 

The  tropical  zone  has  the  least  annual  variation  of 
insolation.  It  has  the  maximum  annual  amount  of 
insolation.  Its  annual  range  of  temperature  is  very 
slight.  It  is  the  summer  zone.  Beyond  the  tropics 
the  contrasts  between  the  seasons  rapidly  become 
more  marked.  The  polar  zones  have  the  greatest 
variation  in  insolation  between  summer  and  win- 
ter. They  also  have  the  minimum  amount  of  insola- 
tion for  the  whole  year.  They  may  well  be  called  the 
winter  zones,  for  their  summer  is  so  short  and  cool 
that  the  heat  is  insufficient  for  most  forms  of  vegeta- 


CLIMATIC  ZONES  AND   SUBDIVISIONS         21 

tion,  especially  for  trees.  The  temperate  zones  are 
intermediate  between  the  tropical  and  the  polar  in 
the  matter  of  annual  amount  and  of  annual  variation 
of  insolation.  Temperate  conditions  do  not  char- 
acterise these  zones  as  a  whole.  They  are  rather  the 
seasonal  belts  of  the  world.  These  five  zones  further 
differ  more  or  less  from  one  another  in  the  character 
of  their  animals  and  plants,  and  in  the  conditions  of 
human  life  within  their  boundaries. 

Taking  the  area  of  a  hemisphere  as  unity,  the  rela- 
tive areas  of  these  zones  are  as  follows: 

Tropical    0.40 

Temperate    0.52 

Polar    - 0.08 

This  subdivision  of  the  earth's  surface  on  the  basis 
of  the  geometrical  distribution  of  sunshine  dates 
from  the  time  of  the  early  Greek  philosophers  and 
geographers,  but  it  is  impossible  to  determine  with 
certainty  just  when  and  by  whom  the  various  sugges- 
tions in  this  connection  were  made.  The  famous 
geographer  Ptolemy,  who  lived  in  the  second  cent- 
ury A.D.,  used  different  schemes  at  different  times.  In 
the  lower  latitudes  the  breadth  of  a  klima,  or  zone, 
was  fixed  by  the  difference  of  a  quarter  of  an  hour  in 
the  length  of  the  longest  day,  but  in  higher  latitudes 
differences  of  half  an  hour,  an  hour,  and  finally  a 
month  were  the  determining  factors. 

Parmenides,  who  flourished  about  the  middle  of 
the  fifth  century  B.  c.,  proposed  a  five-zone  division 
of  the  earth's  surface  not  very  unlike  our  present  sys- 


22  CLIMATE 

tern.  These  zones  were  a  torrid  zone,  uninhabitable 
because  of  heat;  two  frigid  zones,  uninhabitable  be- 
cause of  cold;  and  two  intermediate  zones,  of  moder- 
ate temperature,  suitable  for  man.  The  exact  limits 
assigned  to  these  zones  are  not  known  with  certainty  ; 
but  it  is  reasonable  to  suppose  that  the  Arctic  circle 
was  even  then  recognised  as  a  natural  boundary  for 
the  north  polar  zone,  and  it  is  pretty  clear  that  the 
temperate  zone  was  much  smaller,  and  the  torrid  zone 
much  larger,  than  in  our  present  classification.  (  See 
Fig.  4.) 


FIG.  4.     THE  ZONES  IN 
THE  TIME  OF  PARMENIDES 

The  exact  boundaries  of  the  different  zones  varied 
more  or  less  for  some  time,  as  astronomical  know- 
ledge became  more  and  more  exact,  and  as  the  habit- 
able area  of  the  earth's  surface  was  gradually  ex- 
tended, but  the  scheme  was  generally  adopted  by 
later  writers.  Polybius  (born  about  B.C.  204),  how- 
ever, divided  his  torrid  zone  into  two  parts  by  the 
equator,  and  Posidonius  (born  about  B.C.  135)  di- 
vided his  torrid  zone  into  three  parts,  making  six  and 
seven  zones  respectively.  Aristotle  (born  B.C.  384) 


CLIMATIC  ZONES  AND   SUBDIVISIONS         23 

limited  the  torrid  zone  by  the  tropics,  and  the  north 
temperate  zone  by  the  Arctic  circle ;  but  there  is  doubt 
whether  he  really  meant  the  fixed  Arctic  circle  which 
we  know.  He  believed  both  temperate  zones  habit- 
able, thus  limiting  the  uninhabitable  area  to  the 
astronomical  tropical  zone.  Eudoxus,  of  Cnidus, 
who  lived  about  B.C.  366,  used  a  division  of  a  quadrant 
of  the  earth's  circumference  into  fifteen  parts,  of 
which  four  belonged  to  the  torrid,  five  to  the  temper- 
ate, and  six  to  the  frigid  zone.  The  tropics  were 
thus  fixed  at  latitude  24°.  Strabo  (born  about  B.C. 
54),  opposed  the  prevailing  view  that  the  whole  of 
the  belt  between  the  two  tropics  was  uninhabitable, 
and  also  first  clearly  set  forth  the  opinion  that  the 
temperature  decreases  with  increasing  altitude  above 
sea-level,  as  well  as  with  increasing  latitude.  Strabo 
also  had  some  fairly  distinct  ideas  regarding  local 
differences  of  climate  resulting  from  the  influence  of 
land  and  water  and  of  mountain  barriers,  and  noted 
several  effects  of  climate  upon  man  and  upon  vegeta- 
tion. He  appreciated  the  fact  that  the  zones  were 
zones  of  temperature  as  well  as  zones  of  sunshine. 
As  early  as  about  400  B.C.,  Hippocrates  had  endeav- 
oured to  show  a  causal  relation  between  sunshine  and 
the  topography  of  a  district  on  the  one  hand  and  the 
characteristics  of  its  inhabitants  on  the  other.  He 
also  gave  an  outline  of  geographical  pathology.1 

1  The  older  views  regarding  the  climates  and  the  habitability  of 
the  five  zones  were  thus  stated  by  Virgil  (Georgics,  i,  233-239, 
translation  by  Davidson)  :  "  Five  zones  embrace  the  heavens; 


24  CLIMATE 

Temperature  Zones.  The  classification  of  the 
climatic  zones  on  the  basis  of  the  geometrical  distribu- 
tion of  sunshine  serves  very  well  for  purposes  of 
simple  description,  but  a  glance  at  any  isothermal 
chart  shows  at  once  that  the  isotherms  do  not  coincide 
with  the  latitude  lines.  In  fact,  in  the  higher  lati- 
tudes, the  former  often  follow  the  meridians  more 
closely  than  they  do  the  parallels  of  latitude.  The 
astronomical  zones — i.  e.,  the  zones  of  light — there- 
fore differ  a  good  deal  from  the  zones  of  heat.  Hence 
it  has  naturally  been  suggested  that  the  zones  be  lim- 
ited by  isotherms  rather  than  by  parallels  of  latitude, 
and  that  a  closer  approach  be  thus  made  to  the  actual 
conditions  of  climate. 

Supan  (see  Fig.  5)  has  suggested  limiting  the  hot 
belt,  which  corresponds  to  the  old  torrid  zone,  but  is 
slightly  greater,  by  the  two  mean  annual  isotherms 
of  68° — a  temperature  which  approximately  coin- 
cides with  the  polar  limit  of  the  trade  winds  and 
with  the  polar  limit  of  palms.  The  latter  is  consid- 
ered by  Grisebach  to  be  the  truest  expression  of  a 
tropical  climate.  The  hot  belt  widens  somewhat 
over  the  continents,  chiefly  because  of  the  mobility  of 
the  ocean  waters,  whereby  there  is  a  tendency  towards 
an  equalisation  of  the  temperature  between  equator 

whereof  one  is  ever  glowing  with  the  bright  sun,  and  scorched 
forever  by  his  fire;  round  which  the  two  farthest  ones  to  the  right 
and  left  are  extended,  stiff  with  cerulean  ice  and  horrid  showers. 
Between  these  and  the  middle  zones,  two  by  the  bounty  of  the  gods 
are  given  to  weak  mortals;  and  a  path  is  cut  through  both,  where 
the  series  of  the  signs  might  revolve  obliquely." 


CLIMATIC  ZONES  AND   SUBDIVISIONS 


25 


and  poles  in  the  oceans,  while  the  stable  lands  acquire 
a  temperature  suitable  to  their  own  latitude.  Fur- 
thermore, the  unsymmetrical  distribution  of  land  in 
the  low  latitudes  of  the  northern  and  southern  hemi- 
spheres results  in  an  unsymmetrical  position  of  the  hot 
belt  with  reference  to  the  equator,  the  belt  extending 


FIG.  5.     SUPAN'S  TEMPERATURE  ZONES 

farther  north  than  south  of  the  equator.  The  polar 
limits  of  the  temperate  zones  are  fixed  by  the  isotherm 
of  50°  for  the  warmest  month.  This  is  a  much  more 
satisfactory  limit  than  the  mean  annual  isotherm  of 
32°,  which  has  also  been  suggested;  for  climates  dif- 
fering very  widely  from  one  another  are  found  to 
have  the  same  mean  annual  temperature  of  32°.  The 
latter  value  has  chiefly  a  theoretical  interest,  but  is 
of  some  practical  importance  in  its  relation  to  the 
regions  of  frozen  ground.  Summer  heat  is  more  im- 


26  CLIMATE 

portant  for  vegetation  than  winter  cold;  and  where 
the  warmest  month  has  a  temperature  below  50°, 
cereals  and  forest  trees  do  not  grow,  and  man  has  to 
adjust  himself  to  the  conditions  in  a  very  special  way. 
The  two  polar  caps  are  not  symmetrical  as  regards  the 
latitudes  which  they  occupy.  The  presence  of  ex- 
tended land  masses  in  the  high  northern  latitudes 
carries  the  temperature  of  50°  in  the  warmest  month 
farther  poleward  there  than  is  the  case  in  the  corre- 
sponding latitudes  occupied  by  the  oceans  of  the 
southern  hemisphere,  which  warm  less  easily  and  are 
constantly  in  motion.  Hence  the  southern  cold  cap, 
which  has  its  equatorial  limits  at  about  lat.  50°  S.,  is 
of  much  greater  extent  than  the  northern  polar  cap. 
So  far  as  this  south  polar  zone  is  concerned,  the  pres- 
ence or  absence  of  an  Antarctic  continent  is  imma- 
terial; for  such  a  land  mass  must  be  ice-covered,  and 
hence  cannot  operate  to  raise  the  temperature  as  in 
the  case  of  a  land  surface  to  which  the  sun's  rays  have 
immediate  access.  The  northern  temperate  belt,  in 
which  the  great  land  areas  lie,  is  much  broader  than 
the  southern,  especially  over  the  continents.  These 
temperature  zones  have  real  significance.  They  em- 
phasise the  natural  conditions  of  climate  more  than 
can  be  the  case  in  any  subdivision  by  latitude  circles, 
and  they  bear  a  fairly  close  resemblance  to  the  old 
zonal  classification  of  the  Greeks. 

In  high  latitudes,  neither  the  mean  annual  tempera- 
lure  nor  the  temperature  of  the  coldest  month  is 
nearly  as  important  a  climatic  control  over  vegetation 


28  CLIMATE 

as  is  the  temperature  of  summer,  from  the  point  of 
view  of  climate  as  a  whole,  and  especially  in  relation 
to  organic  life.  The  summer  temperatures  deter- 
mine habitability,  the  limits  of  plant  growth,  and  the 
general  conditions  of  human  life.  Hence,  in  the 
higher  latitudes,  zones  bounded  by  mean  annual 
isotherms  are  no  great  improvement  over  zones  limited 
by  latitude  circles. 

Another  classification  of  temperature  zones  has 
been  suggested  by  Koppen  (see  Fig.  6).  In  this, 
the  length  of  time  during  which  the  tempera- 
ture remains  within  certain  fixed  limits,  these  limits 
having  well-marked  relations  to  organic  life,  is  taken 
into  account.  Two  critical  daily  mean  temperatures, 
68°  and  50°,  and  the  duration  of  these  temperatures 
for  periods  of  one,  four,  and  twelve  months,  are  the 
factors  in  this  classification.  These  temperatures  are 
not  reduced  to  sea-level.  A  normal  duration  of  a 
temperature  of  50°  for  less  than  a  month  fixes  very 
well  the  polar  limit  of  trees  and  the  limits  of  agricul- 
ture. Near  this  line  are  found  the  last  groups  of 
trees  in  the  tundras.  A  temperature  of  50°  for  four 
months  marks  the  limit  of  the  oak,  and  also  closely 
coincides  with  the  limits  of  wheat  cultivation.  North 
of  the  tree  limit,  agriculture  ceases,  and  man's  food  is 
to  be  sought  very  largely  in  the  sea.  With  the  ap- 
proach to  this  line,  the  period  of  plant  growth  is 
shortened  more  and  more,  agricultural  operations  be- 
come restricted,  and  occupations  of  other  kinds  are 
followed.  These  critical  temperatures  and  their 


CLIMATIC  ZONES  AND   SUBDIVISIONS         29 

varying  periods  of  duration  form  the  basis  of  the  fol- 
lowing classification: 

1.  Tropical  belt:  all  months  hot  (over  68°).  This 
is  almost  altogether  within  the  tropics;  it  reaches,  in 
round  numbers,  from  latitude  20°  N.  to  16  S. 

2.  Sub-tropical  belts:  4  to  11  months  hot   (over 
68°)  ;  1  to  8  months  temperate  (50°-68°.) 

3.  Temperate  belts:  4  to  12  months  temperate. 

4.  Cold  belts:  1  to  4  months  temperate;  the  rest 
cold  (below  50°). 

5.  Polar  belts:  all  months  cold. 

The  temperate  belts  of  both  hemispheres  are 
further  subdivided  into  three  districts  *-  —the  steadily 
temperate  belt 2  is  found  only  on  the  oceans ;  the  belt 
of  hot  summers  3  only  on  the  continents ;  and  the  third, 
with  moderate  summers  and  cold  winters,4  extends 
around  the  world,  with  the  exception  of  a  notable  in- 
terruption over  Siberia. 

In  the  second  of  these  subdivisions,  except  in  east- 
ern North  America  and  Asia,  the  rainfall  is  generally 
deficient;  irrigation  is  more  or  less  necessary,  and 
deserts  and  steppes  characterise  the  continental  por- 
tions. Only  in  the  monsoon  districts  of  southern  and 
eastern  Asia,  of  Brazil,  and  of  south-eastern  North 
America,  do  we  find  high  temperatures  combined  with 

1  All  characterised  by  having  at  least  four  months  temperate 
(50°-68°),  and  not  more  than  four  months  hot  (over  68°). 

2  No  month  over  68°  or  below  50°. 

3  Has  temperatures  below  50°  for  one  or  more  months. 

4  Separated  from  "permanently  temperate"  by  the  50°  isotherm  for  the 
coldest,  and  from  "hot  summers"  by  the  71.  6°  (22°  C.)  isotherm  for  the 
warmest  monttt 


30  CLIMATE 

high  relative  humidity.  The  third  subdivision  above 
noted  is  now  the  chief  seat  of  human  development. 
Over  a  large  part  of  the  cold  belt  of  the  northern 
hemisphere,  the  ground  is  permanently  frozen,  thaw- 
ing only  a  little  on  the  surface  in  summer.  Never- 
theless, in  portions  of  it  trees  and  hardy  cereals  grow. 
The  polar  belts  are,  as  a  whole,  outside  the  limits  of 
tree  growth. 

Another  suggestion  has  been  made  by  Gebelin,  who 
has  proposed  to  select,  as  limits  of  the  temperate  zone, 
certain  visible  geographical  boundaries,  in  contrast 
with  the  ideal  climatic  limits  based  upon  the  distribu- 
tion of  sunshine.  On  the  oceans,  the  tropical  circles 
serve  as  acceptable  boundaries  on  the  sides  towards 
the  equator,  but  on  the  continents  the  desert  belts  on 
both  sides  of  the  tropics  are  reasonable  limits,  although 
these  deserts  do  not  reach  the  eastern  coasts  of  the 
continents.  For  the  polar  limits  of  the  temperate 
zone,  the  tundras  are  chosen  on  the  continents,  and  the 
summer  ice-masses  on  the  oceans. 

Wind  Zones.  While  a  simple  classification  of  the 
zones  on  the  basis  of  temperature  is  an  improvement 
upon  any  rigid  scheme  of  division  by  latitude  circles, 
the  heat  zones  emphasise  the  element  of  temperature 
to  the  exclusion  of  such  important  elements  as  winds 
and  rainfall.  So  distinctive  are  the  larger  climatic 
features  of  the  great  wind -belts  of  the  world,  that  a 
classification  of  climates  according  to  wind  systems 
has  been  suggested  by  Davis.  As  the  rain  belts  of 
the  world  are  closely  associated  with  these  wind  sys- 


CLIMATIC  ZONES  AND   SUBDIVISIONS         31 

terns,  a  classification  of  the  zones  by  winds  also  em- 
phasises the  conditions  of  rainfall.  In  such  a  scheme, 
the  torrid,  or  tropical  zone,  with  its  regularity  of 
weather  through  the  year,  and  the  comparative  sim- 
plicity of  its  climatic  features,  is  bounded  on  the  north 
and  south  by  the  margins  of  the  trade  wind  belts,  and 
is  therefore  larger  than  the  classic  torrid  zone.  This 
trade  wind  zone  is  somewhat  wider  on  the  eastern  side 
of  the  oceans,  and  properly  includes  within  its  limits 
the  equable  marine  climates  of  the  eastern  margins 
of  the  ocean  basins,  even  as  far  north  as  latitude  30° 
or  35°. 

Most  of  the  eastern  coasts  of  China  and  of  the 
United  States  are  thus  left  in  the  more  rigorous  and 
more  variable  conditions  of  the  north  temperate  zone. 
Through  the  middle  of  the  trade  wind  zone  extends 
the  sub-equatorial  belt,  with  its  migrating  calms,  rains, 
and  monsoons.  On  the  polar  margins  of  the  trade 
wind  zone  lie  the  sub-tropical  belts,  of  alternating 
trades  and  westerlies.  The  temperate  zones,  with  the 
great  irregularity  of  their  weather  phenomena  and 
their  marked  seasonal  changes,  embrace  the  latitudes 
of  the  stormy  westerly  winds,  having  on  the  equator- 
ward  margins  the  sub-tropical  belts,  and  being  some- 
what narrower  than  the  classic  temperate  zones. 
Towards  the  poles,  there  is  no  obvious  limit  to  the  tem- 
perate zones,  for  the  prevailing  westerlies  extend 
beyond  the  polar  circles.  These  circles  may,  how- 
ever, serve  fairly  well  as  boundaries,  because  of  their 
importance  from  the  point  of  view  of  insolation.  The 


32  CLIMATE 

polar  zones  in  the  wind  classification,  therefore,  re- 
main just  as  in  the  older  five-zone  scheme. 

A  compromise  between  the  rigid  division  by  lati- 
tude circles  and  the  isothermal  and  wind  classifica- 
tions has  been  suggested  by  Woeikof,  who  objects  to 
limiting  the  torrid  zone  by  the  tropics  on  the  ground 
that  the  high  temperatures  of  that  zone,  as  well  as 
its  characteristic  winds,  extend  beyond  these  parallels. 
Latitude  30°  would  be  a  more  natural  boundary ; 'but 
as  the  westerlies,  which  are  characteristic  of  the  tem- 
perate zones,  prevail  there  in  winter,  latitude  25°  is 
chosen  as  a  compromise  between  23^/2°  and  30°.  -The 
polar  zones  are  bounded  by  latitude  65°.  When 
bounded  by  these  several  limits,  the  areas  of  the'  dif- 
ferent zones  are  as  follows:  L 

Tropical  Zone 417 

Temperate   Zones 490 

Polar  Zones..  93 


1000 

Summary  and  Conclusions.  Reviewing  what  has 
been  said  regarding  the  climatic  zones,  it  would  seem 
that,  all  things  considered,  ajsimple  division  by  iso- 
therms, such  as  that  suggested  by  Supan"  (1896),  is 
the  best  for  general  use^  The  early  division  by -lati- 
tude circles,  while  it  has  the  merits  of  great  simplicity, 
and  emphasises  the  all-important  element  of  sunshine, 
is  too  arbitrary,  and  hence  does  not  accord  sufficiently 
well  with  the  facts  of  actual  climate.  Nevertheless,  we 
should  not  discard  the  classic  zones  without  recog- 


CLIMATIC  ZONES  AND  SUBDIVISIONS         33 

nising  that  they  have  a  real  meaning  in  relation  to 
solar  climate.  The  grouping  of  the  climatic  zones 
according  to  wind  systems  has  much  to  recommend  it 
from  a  meteorological  standpoint,  but  is  not  quite 
simple  enough  for  general  use.  Its  adoption  involves 
an  understanding  of  the  great  wind  and  calm  belts  of 
the  world,  and  of  the  migration  of  these  belts.  The 
shifting  of  the  boundaries  of  the  torrid  zone  also 
brings  in  an  element  of  uncertainty  which  is  some- 
what confusing,  although,  as  a  place  in  the  sub-tropi- 
cal belt  really  changes  its  climate  with  the  seasonal 
change  from  westerlies  to  trades,  and  vice  versa,  it 
may  reasonably  be  expected  to  change  its  zone.  In 
other  words,  actual  climatic  conditions  are  recognised ; 
and  in  any  case,  this  is  a  more  reasonable  plan  than  to 
limit  the  torrid  zone  by  means  of  the  tropics,  which 
arbitrarily  cut  across  the  trade  wind  belts  and  sepa- 
rate areas  which  are  climatically  the  same.  The  tem- 
perature zones  proposed  by  Koppen,  while  useful  in 
special  studies  of  plant  distribution,  are  too  detailed 
for  general  adoption. 

Whatever  climatic  zones  we  adopt,  we  shoul'd  cer- 
tainly abandon  the  word  temperate  altogether  as  the 
designation  of  the  middle  zone  in  each  hemisphere, 
and  substitute  some  such  adjective  as  intermediate 
for  it.  The  words  torrid  and  frigid  should  likewise 
disappear,  and  be  replaced  by  tropical  or  equatorial, 
and  polar. 

Necessary  Subdivisions  of  the  Zones.  However 
we  may  classify  them,  the  climatic  zones  are  far  from 


34  CLIMATE 

being  uniform  in  character  throughout  their  whole 
extent.  Hence,  no  brief,  simple  description  of  the 
climate  of  a  zone  can  be  given.  For  this  reason,  sug- 
gestions have  been  made  regarding  subdivisions  of 
the  different  zones.  Thus,  in  the  case  of  the  classic 
north  temperate  zone,  it  has  been  proposed  to  subdi- 
vide it  into  sub-tropical,  temperate,  and  sub-arctic,  but 
the  question  how  to  limit  these  subdivisions  is  difficult 
to  settle.  A  more  rational  scheme  is  that  which,  in 
view  of  the  great  differences  in  the  climatic  relations 
of  land  and  water,  recognises  a  first  large  subdivision 
of  each  zone  into  land  and  water  areas.  Then,  as  con- 
tinental interiors  differ  from  coasts,  and  as  windward 
coasts  have  climates  unlike  those  of  leeward  coasts,  a 
further  natural  subdivision  would  separate  these  dif- 
ferent areas.  Finally,  the  control  of  altitude  over 
climate  is  so  marked  that  plateaus  and  mountains 
may  well  be  set  apart  by  themselves  as  separate  clima- 
tic districts.  If  each  of  the  zones,  whether  bounded 
by  latitude  circles,  or  by  isotherms,  or  by  wind  sys- 
tems, be  considered  under  these  general  subdivisions, 
as  close  an  approach  to  actual  conditions  of  climate 
will  be  made  as  is  possible  in  general  description.  Ob- 
viously, however,  when  the  larger  zones  are  subdi- 
vided to  such  an  extent  as  is  here  suggested,  we  are 
dealing  with  a  classification  of  climates  rather  than 
with  climatic  zones. 


CHAPTER  II 

THE  CLASSIFICATION  OF  CLIMATES 

Need  of  a  Classification  of  Climates — Relation  of  Continental  and 
Ocean  Areas  to  Temperature:  Reasons  for  the  Slow  Change  in 
the  Temperature  of  Ocean  Waters — Marine  or  Oceanic  Cli-r 
mate — Continental  Climate — Desert  Climate — Coast  or  Lit- 
toral Climate — Monsoon  Climate — Mountain  and  Plateau 
Climate — Mountains  as  Climatic  Divides. 

Need  of  a  Classification  of  Climates.  A  broad  di- 
vision of  the  earth's  surface  into  zones  is  necessary  as 
a  first  step  in  any  systematic  study  of  climate,  but  it 
is  not  satisfactory  when  a  more  detailed  discussion  is 
undertaken.  The  reaction  of  the  physical  features 
of  the  earth's  surface  upon  the  atmosphere  compli- 
cates the  climatic  conditions  found  in  each  of  the 
zones,  and  makes  further  subdivision  desirable.  Un- 
der the  control  of  these  different  physical  conditions, 
the  climatic  elements  unite  to  produce  certain  fairly 
distinct  types  of  climate,  and  these  may  be  classified 
in  various  ways.  The  usual  method  is  to  separate 
the  continental  (near  sea-level)  and  the  marine.  An 
extreme  variety  of  the  continental  is  the  desert;  a 
modified  form,  the  littoral;  while  altitude  is  so  im- 
portant a  control  that  mountain  and  plateau  climates 
are  further  grouped  by  themselves, 

35 


36  CLIMATE 

Relation  of  Continental  and  Ocean  Areas  to  Tem- 
perature. Land  and  water  differ  greatly  in  their  be- 
haviour regarding  absorption  and  radiation.  The 
former  warms  and  cools  readily,  and  to  a  considerable 
degree;  the  latter,  slowly  and  but  little.  (1)  Of  the 
insolation  which  falls  upon  the  ocean,  a  good  deal  is 
at  once  reflected,  and  is  therefore  not  available  for 
warming  the  water.  Land  surfaces,  on  the  other 
hand,  are  poor  reflectors;  but  little  insolation  is  lost 
in  that  way ;  hence  more  energy  is  available  for  raising 
their  temperature.  (2)  Most  of  the  insolation  which 
enters  the  water  is  transmitted  to  some  depth,  and, 
therefore,  is  not  effectively  applied  to  warming  the 
surface.  Land  is  opaque  and  does  not  allow  the  in- 
cident insolation  to  pass  beyond  a  comparatively  thin 
surface  stratum;  hence  this  surface  can  be  well 
warmed.  (3)  The  evaporation  of  water  requires  a 
large  amount  of  energy,  which  changes  the  state  of 
the  water  without  raising  its  temperature  (latent 
heat).  Land,  although  often  moist,  is  itself  non- 
volatile ;  therefore  the  loss  of  energy  in  the  process  of 
evaporation  is  usually  very  slight.  (4)  Water  is 
more  difficult  to  warm  than  any  other  natural  sub- 
stance, while  land  is  warmed  easily  and  quickly.  If 
equal  amounts  of  heat  are  received  by  equal  areas  of 
land  and  water,  the  former  warms  about  twice  as  much 
as  the  latter.  (5)  The  mobility  of  water  keeps  the 
warmer  and  the  colder  portions  well  mixed,  and  there- 
fore greatly  retards  the  process  of  warming  any  one 
portion  of  the  surface.  Land  cannot  thus  equalise 


TEE  CLASSIFICATION  OF  CLIMATES  37 

its  temperature.  (6)  The  cloudiness  over  the  oceans 
is  usually  greater  than  that  over  the  lands,  and  this 
operates  to  shade  the  former  more  than  the  latter,  re- 
ducing the  energy  available  for  warming  the  water 
surface.  For  these  various  reasons,  ocean  surfaces 
can  warm  but  little  during  the  day,  or  in  summer, 
and  can  cool  but  little  during  the  night,  or  in  winter. 
They,  and  the  air  over  them,  are  therefore  conserva- 
tive as  regards  their  temperatures.  Land  areas,  and 
the  air  over  the  lands,  on  the  other  hand,  warm  and 
cool  readily.  The  influence  of  latitude,  as  seen  in 
solar  climate,  is  not  infrequently  wholly  overcome  by 
the  influence  of  land  and  water. 

Marine  or  Oceanic  Climate.  Conservatism  in  its 
temperature  conditions  is  the  most  distinctive  feature 
of  a  marine  climate.  The  results  of  the  Challen- 
ger Expedition  show  that  the  diurnal  range  of  air 
temperature  over  the  ocean  between  latitudes  0°  and 
40°  averages  only  2°  or  3°.  Further,  the  slow 
changes  in  temperature  of  the  ocean  waters  involve 
a  retardation  in  the  times  of  occurrence  of  the  maxima 
and  minima,  and  a  marine  climate,  therefore,  has 
characteristically  a  cold  spring  and  a  warm  autumn, 
the  seasonal  changes  of  temperature  being  but  slight. 
The  surface  waters  of  oceans  and  lakes  average  some- 
what warmer  than  the  air  over  them,  and  for  this 
reason  all  considerable  bodies  of  water  which  remain 
unfrozen  in  winter  become  sources  of  warmth  for  the 
adjacent  lands  during  the  colder  months.  Character- 
istic, also,  of  marine  climates  is  a  prevailingly  higher 


38  CLIMATE 

relative  humidity,  a  larger  amount  of  cloudiness,  and 
a  heavier  rainfall  than  is  found  over  continental  inter- 
iors. All  of  these  features  have  their  explanation  in 
the  abundant  evaporation  from  the  ocean  surfaces. 
In  the  middle  latitudes,  again,  there  is  this  contrast 
between  the  oceans  and  the  continental  interiors,  that 
the  former  have  distinctly  rainy  winters,  while  over 
the  latter  the  colder  months  have  a  minimum  of  pre- 
cipitation. Ocean  air  is  cleaner  and  purer  than  land 
air,  and  ocean  air  is,  on  the  wiiole,  in  more  active  mo- 
tion, because  friction  of  air  on  water  is  less  than 
friction  of  air  on  land. 

It  is  obvious  that  an  equable,  damp,  and  cloudy 
climate,  such  as  that  which  is,  on  the  whole,  typical  of 
the  oceans  and  of  their  leeward  coasts,  must  affect 
vegetation  in  a  way  quite  different  from  that  noted 
in  a  hotter  and  drier  climate,  with  greater  variations 
of  temperature.  Thus  Schindler  has  shown  that 
wheat  contains  less  protein  in  a  marine  climate,  and 
hence  more  meat,  leguminous  plants,  and  other  nitro- 
genous foods  are  necessarily  eaten.  An  interior 
climate,  like  that  of  southern  Russia  and  Hungary, 
produces  wheat  which  is  richer  in  protein ;  the  need  of 
other  nitrogenous  foods  is  consequently  decreased. 
The  proportion  of  starch  is  decreased,  and  that  of 
gluten  is  increased,  in  a  hot,  dry  climate.  The  size 
of  the  crop  is  also  affected  by  the  climate. 

Continental  Climate.  Marine  climate  is  equable; 
continental,  is  severe.  The  annual  temperature 
ranges  increase,  as  a  whole,  with  increasing  distance 


THE  CLASSIFICATION  OF  CLIMATES  39 


from  the  ocean;  the  regular  diurnal  ranges  are  also 
large,  reaching  35°  or  40°,  and  even  more,  in  the  arid 

J.  F.  M.  A.  M.  J.  J.  A.  S.  0.  N.  D.  J. 

F.  ' 


86° 


J.  F.  M.  A.  M.  J.  J.  A.  S.  0.  N.  D.  J. 


FIG.  7.     INFLUENCE  OF  LAND  AND  WATER  ON  THE 
ANNUAL  MARCH  OF  AIR  TEMPERATURE 

continental    interiors.     The    coldest    and    warmest 
months  are  usually  January  and  July,  the  times  of 


40  CLIMATE 

maximum  and  minimum  temperatures  being  less  re- 
tarded than  in  the  case  of  marine  climates.  April  is 
usually  warmer  than  October,  unless  spring  warm- 
ing is  delayed  by  the  melting  of  a  snow-cover.  In 
the  latter  case,  the  snow-covered  land  surface  tem- 
porarily takes  on  the  characteristics  of  a  water 
surface,  and  has  a  retarded  spring.  The  greater  sea- 
sonal contrasts  in  temperature  over  the  continents 
than  over  the  oceans  are  furthered  by  the  less  cloudi- 
ness over  the  former.  The  clearer  continental  skies 
of  high  latitudes  favour  a  lowering  of  the  winter,  but 
a  slight  rise  of  the  summer  temperatures,  while  in 
lower  latitudes  the  clearer  summer  skies  favour  a 
higher  mean  annual  temperature.  Diurnal  and  an- 
nual changes  of  nearly  all  the  elements  of  climate  are 
greater  over  continents  than  over  oceans;  and  this 
holds  true  of  irregular,  as  well  as  of  regular,  varia- 
tions. The  contrast  between  marine  and  continental 
climates  in  the  matter  of  the  annual  march  of  tem- 
perature is  shown  in  Figure  7.  In  low  latitudes,  the 
curve  for  Funchal,  on  the  island  of  Madeira  (M), 
represents  the  marine  type,  and  that  for  Bagdad,  in 
Asia  Minor  (Bd),  the  continental.  For  higher  lati- 
tudes, the  curves  for  Valentia  (V),  a  coast  station 
in  the  south-west  of  Ireland,  and  for  Nerchinsk  (N), 
in  eastern  Siberia,  are  representatives  of  the  two 
types. 

Owing  to  the  distance  from  the  chief  source  of 
supply  of  water-vapour — the  oceans — the  air  over 
the  larger  land  areas  is  naturally  drier  and  dustier 


THE  CLASSIFICATION  OF  CLIMATES  41 

than  that  over  the  oceans.  Yet  even  in  the  arid  con- 
tinental interiors  in  summer,  the  absolute  vapour  con- 
tent is  surprisingly  large,  although  the  air  is  still  far 
from  being  saturated.  In  the  hottest  months  the 
percentages  of  relative  humidity  may  reach  20%  or 
30%.  At  the  low  temperatures  which  prevail  in  the 
winter  of  the  higher  latitudes,  the  absolute  humidity 
is  very  low,  but,  owing  to  the  cold,  the  air  is  often 
damp.  Cloudiness,  as  a  rule,  decreases  inland,  reach- 
ing its  minimum  in  deserts.  And  with  this  lower 
relative  humidity,  more  abundant  sunshine  and  higher 
temperature,  the  evaporating  power  of  a  continental 
climate  is  much  greater  than  that  of  the  more  humid, 
cloudier,  and  cooler  marine  climate.  Actual  evapo- 
ration is,  however,  under  these  conditions,  usually 
much  less  than  the  possible  evaporation  which  would 
take  place  were  there  more  water  present  to  be 
evaporated.  Both  amount  and  frequency  of  rain- 
fall, as  a  rule,  decrease  inland,  but  the  conditions  are 
very  largely  controlled  by  local  topography  and  by 
the  prevailing  winds.  The  decreased  frequency  of 
rainfall  on  the  lowlands  is  especially  marked  in  win- 
ter. Winds  average  somewhat  lower  in  velocity, 
and  calms  are  more  frequent,  over  continents  than 
over  oceans.  The  seasonal  changes  of  pressure  over 
the  former  give  rise  to  systems  of  inflowing  and  out- 
flowing, so-called  continental,  winds,  sometimes  so 
well  developed  as  to  become  true  monsoons.  Usu- 
ally, however,  the  changes  in  direction  and  the  de- 
velopment are  not  very  marked. 


42  CLIMATE 

In  winter,  clear,  crisp  days,  which  are  followed  by 
cold,  calm  nights,  and  interrupted  from  time  to  time 
by  spells  of  cloudy,  windy  weather,  with  or  without 
light  precipitation;  in  summer,  clear,  calm  nights, 
followed  by  hot  days  with  increasing  wind  velocity 
and  heavy  clouds  towards  noon,  and  often  by  thun- 
derstorms later  in  the  afternoon — these  are  typical 
weather  conditions  of  continental  interiors  in  the 
higher  latitudes;  and  they  are  of  much  interest  to 
man.  The  extreme  temperature  changes  which  oc- 
cur over  the  continents  are  the  more  easily  borne  be- 
cause of  the  dryness  of  the  air;  because  the  minimum 
temperatures  of  winter  occur  when  there  is  little  or 
no  wind,  and  because,  during  the  warmer  hours  of  the 
summer,  there  is  the  most  air  movement. 

Desert  Climate.  An  extreme  type  of  continental 
climate  may  be  found  in  deserts.  It  is  a  curious  fact 
that  desert  and  marine  climates — the  two  extremes  of 
the  climatic  scale — resemble  one  another  in  some  re- 
spects. Desert  air,  though  often  dusty  by  day,  is 
notably  free  from  micro-organisms;  the  purity  of 
ocean  air  is  well  known.  Again,  deserts  and  oceans 
alike  have  high  wind  velocities.  The  large  diurnal 
temperature  ranges  of  inland  regions,  which  are 
most  marked  where  there  is  little  or  no  vegetation, 
give  rise  to  active  convectional  currents  during 
the  warmer  hours  of  the  day.  Hence  high  winds, 
disagreeable  because  of  the  dust  and  sand  which  they 
carry,  are  common  by  day,  while  the  nights  are  apt 
to  be  calm  and  relatively  cool.  Travelling  by  day  is 


THE  CLASSIFICATION  OF  CLIMATES  43 

unpleasant  under  such  conditions.  Diurnal  cumu- 
lus clouds,  often  absent  because  of  the  excessive  dry- 
ness  of  the  air,  are  thus  replaced  by  clouds  of  blowing 
dust  and  sand.  This  sand,  often  carried  afar,  may 
find  a  resting-place  on  the  moister  lands  to  leeward. 
Thus  beds  of  loess  are  formed.  Indeed,  many  geo- 
logical phenomena,  and  special  physiographic  types 
of  varied  kinds,  are  associated  with  the  peculiar  con- 
ditions of  desert  climate.  The  excessive  diurnal 
ranges  of  temperature  cause  rocks  to  split  and  break 
up.  Wind-driven  sand  erodes  and  polishes  the  rocks. 
When  the  separate  fragments  become  small  enough, 
they,  in  their  turn,  are  transported  by  the  winds  and 
further  eroded  by  friction  during  their  journey.  The 
ground  is  often  swept  clean  by  the  winds.  Curious 
conditions  of  drainage  result  from  the  deficiency  in 
rainfall.  Rivers  "  wither  "  away,  or  end  in  sinks  or 
brackish  lakes.  Desert  plants  protect  themselves 
against  the  attacks  of  animals  by  means  of  thorns, 
and  against  evaporation  by  means  of  hard  surfaces 
and  an  absence  of  leaves.  The  life  of  man  in  the  des- 
ert is  likewise  strikingly  controlled  by  the  climatic 
peculiarities  of  strong  sunshine,  of  heat,  and  of  dust. 
Occasionally  heavy  downpours  of  rain  (cloud-bursts) 
over  mountains  or  on  the  borders  of  deserts,  cause 
sudden  floods.  Even  slight  rainfalls  in  deserts 
awaken  multitudes  of  dormant  plant  seeds. 

Coast  or  Littoral  Climate.  Between  the  pure 
marine  and  the  pure  continental  types,  the  coasts  fur- 
nish almost  every  grade  of  transition.  Hence  coast 


44  CLIMATE 

or  littoral  climates  may  well  be  placed  in  a  group  by 
themselves.  Prevailing  winds  are  here  important 
controls.  When  these  blow  from  the  ocean,  as  on  the 
western  coasts  of  the  temperate  zones,  the  climates 
are  more  marine  in  character ;  but  when  they  are  off- 
shore, as  on  the  eastern  coasts  of  these  same  zones,  a 
somewhat  modified  type  of  continental  climate  pre- 
vails, even  up  to  the  immediate  sea-coast.  Hence  the 
former  have  a  much  smaller  range  of  temperature; 
their  summers  are  more  moderate  and  their  winters 
milder;  extreme  temperatures  are  very  rare;  the  air 
is  damp ;  there  is  much  cloud.  All  these  marine  feat- 
ures diminish  with  increasing  distance  from  the  ocean, 
especially  when  there  are  mountain  ranges  near  the 
coast,  as  is  the  case  in  the  western  United  States  and 
in  Scandinavia.  In  the  tropics,  windward  coasts  are 
usually  well  supplied  with  rainfall,  and  the  tempera- 
tures are  modified  by  sea  breezes.  Leeward  coasts 
in  the  trade  wind  belts  offer  special  conditions.  Here 
the  deserts  often  reach  the  sea,  as  on  the  western  coasts 
of  South  America,  Africa,  and  Australia.  Cold  ocean 
currents,  with  prevailing  winds  along  shore  rathej* 
than  onshore,  are  here  hostile  to  rainfall,  although 
the  lower  air  is  often  damp,  and  fog  and  cloud  are 
not  uncommon. 

Monsoon  Climate.  Exceptions  to  the  general  rule 
of  rainier  eastern  coasts  in  trade  wrind  latitudes  are 
found  in  the  monsoon  regions,  as  in  India,  for  ex- 
ample, where  the  western  coast  of  the  peninsula  is 
abundantly  watered  by  the  wet  south-west  monsoon. 


THE  CLASSIFICATION  OF  CLIMATES  45 

As  monsoons  often  sweep  over  large  districts,  not 
only  coast  but  interior,  a  separate  group  of  monsoon 
climates  is  desirable.  In  India,  there  are  really  three 
seasons — one  cold,  during  the  winter  monsoon;  one 
hot,  in  the  transition  season;  and  one  wet,  during  the 
summer  monsoon.  Little  precipitation  occurs  in 
winter,  and  that  chiefly  in  the  northern  provinces. 
The  high  temperatures  of  the  transition  periods  are 
most  oppressive  when  the  air  is  most  damp.  In  India 
this  is  the  case  in  the  autumn.  In  low  latitudes,  mon- 
soon and  non-monsoon  climates  differ  but  little,  for 
summer  monsoons  and  regular  trade  winds  both  give 
rains,  and  wind  direction  has  slight  effect  upon 
temperature. 

The  winter  monsoon  is  offshore,  and  the  summer 
monsoon  onshore,  under  typical  conditions,  as  in 
India.  But  exceptional  cases  are  found  where  the 
opposite  is  true.  Thus,  on  the  north-western  coast  of 
Japan,  the  north-eastern  coasts  of  Formosa  and  of  the 
Philippines,  and  the  eastern  coasts  of  the  southern 
Deccan  and  of  Ceylon,  the  prevailing  offshore,  winter, 
dry  monsoon  becomes  an  onshore,  rainy  wind.  Many 
complicated  cases  of  this  kind  are  not  easily  co-ordi- 
nated. In  higher  latitudes,  the  seasonal  changes  of 
the  winds,  although  not  truly  monsoonal,  involve  dif- 
ferences in  temperature  and  in  other  climatic  ele- 
ments. The  eastern  coast  of  the  United  States  has 
prevailing  cold,  dry,  clear  winds  from  the  continental 
interior  in  winter,  while  the  prevailing  winds  of  sum- 
mer are  south-west,  and  hence  warm  and  often  moist. 


46  CLIMATE 

The  only  well-developed  monsoons  on  the  coast  of  the 
continents  of  higher  latitudes  are  those  of  eastern 
Asia.  These  are  offshore  during  the  winter,  giving 
dry,  clear,  and  cold  weather;  while  the  onshore  move- 
ment in  summer  gives  cool,  damp,  and  cloudy 
weather.  Without  these  seasonal  winds  the  winters 
would  have  the  maximum  amount  of  rain  and  cloud. 

Mountain  and  Plateau  Climate.  Both  by  reason 
of  their  actual  height  and  because  of  their  obstructive 
effects,  mountains  influence  climate  similarly  in  all 
the  zones.  Hence  mountain  and  plateau  climates 
are  placed  in  a  group  by  themselves,  as  distinguished 
from  those  of  lowlands.  The  former,  as  contrasted 
with  the  latter,  are  characterised  by  a  decrease  in 
pressure,  temperature,  and  absolute  humidity;  an  in- 
creased intensity  of  insolation  and  radiation;  larger 
ranges  in  soil  temperature;  usually  a  greater  fre- 
quency of  percipitation,  and,  up  to  a  certain  altitude, 
more  of  it. 

At  an  altitude  of  16,000  ft.,  more  or  less,  pressure 
is  reduced  to  about  one-half  of  its  sea-level  value. 
The  highest  human  habitations  are  found  under  these 
conditions.  While  the  pressures  and  the  pressure 
changes  at  sea-level  have  no  marked  effect  upon  man, 
the  physiological  effects  of  the  decreased  pressure 
aloft  (faintness,  nausea,  headache,  weakness)  are  ex- 
perienced by  a  majoritv  of  people  at  altitudes  above 
12,000  to  15,000  ft.  The  symptoms,  and  the  height 
at  which  they  appear,  vary  much  in  different  cases, 
and  depend  upon  the  physical  condition  of  the  indi- 


THE  CLASSIFICATION  OF  CLIMATES  47 

vidual,  the  weather,  bodily  exertion,  and  so  on.  The 
greatest  altitudes  attained  by  man  were  reached  by 
balloon,  and  in  such  cases  a  supply  of  oxygen  is  usu- 
ally taken  up  by  the  aeronaut.  Man  endures  the 
rapid  pressure  changes  during  balloon  ascents  with 
difficulty,  and  often  only  with  considerable  suffering. 
The  eagle  and  the  condor,  however,  suffer  no  incon- 
venience during  their  high  flights. 

It  has  been  suggested  by  Jourdanet  that  mountain 
and  plateau  climates  be  divided  into  groups,  climats 
de  montagne,  below  6500  feet,  and  climats  A3 altitude, 
above  that  height.  The  former  are  beneficial  because 
of  the  stimulating  quality  of  their  clean,  cool  air;  the 
latter  may  be  injurious  because  of  the  low  pressure. 
The  variations  in  pressure,  as  well  as  the  actual  press- 
ures, diminish  aloft.  On  high  mountains  and  plat- 
eaus, the  pressure  is  lower  in  winter  than  in  summer, 
owing  to  the  fact  that  the  atmosphere  is  compressed 
by  cold  to  lower  levels  in  the  winter,  and  is  expanded 
upwards  in  summer  by  heat.  The  morning  minimum 
pressure  on  mountains  is  usually  the  primary  mini- 
mum, the  afternoon  minimum  being  less  marked  and 
coming  later  than  on  lowlands.  Figure  8  shows  the 
diurnal  variation  of  pressure  at  Geneva  (408  meters, 
G),  Berne  (573  meters,  B),  on  the  Santis  (2467 
meters,  S),  and  on  the  summit  of  Mont  Blanc  (4811 
meters,  MB ) ,  and  illustrates  well  the  general  char- 
acteristics of  the  curves  found  at  different  altitudes. 
Local  topography,  however,  is  an  important  control- 
ling influence,  and  modifies  such  curves  very  much. 


48 


CLIMATE 


The  intensity  of  insolation  and  of  radiation  both 
increase  aloft  in  the  cleaner,  purer,  drier,  and  thinner 
air  of  mountain  climates.  The  sun  usually  shines  more 
often  and  more  powerfully  at  high  altitudes.  The 


NOON 


I61?          20* 


24* 


Inches 
.02 

0 
02 

0 
X)2 


JD2 


J02 


M.B 


MB" 


Inches 
.02 

0 

.02 

0 

.02 

0 

.02 

0 

.02 

.04 


Oh  4h  &        NOON         161?          20h  24h 

FIG.  8.     DIURNAL  VARIATION  OF  PRESSURE  :  INFLUENCE  OF  ALTITUDE 

intensity  of  the  sun's  rays  attracts  the  attention  of 
mountain-climbers  at  great  altitudes.  The  excess  of 
surface  temperature  over  air  temperature  also  in- 
creases aloft,  and  is  a  favourable  element  in  plant 
growth.  There  is  likewise  an  increase  in  the  range  of 
surface  temperature,  although  this  is  much  influenced 


THE  CLASSIFICATION  OF  CLIMATES  49 

by  exposure.  The  vertical  decrease  of  temperature, 
which  is  also  much  affected  by  local  conditions,  is  es- 
pecially rapid  during  the  warmer  months  and  hours; 
mountains  are  then  cooler  than  lowlands.  The  in- 
versions of  temperature  characteristic  of  the  colder 
months,  and  of  the  night,  give  mountains  the  advan- 
tage of  higher  temperature  then,  a  fact  of  importance 
in  connection  with  the  use  of  mountains  as  winter  re- 
sorts. At  such  times,  the  cold  air  flows  down  the 
mountain  sides  and  collects  in  the  valleys  below,  be- 
ing replaced  by  warmer  air  aloft.  Hence  diurnal 
and  annual  ranges  of  temperature  on  the  mountain 
tops  of  middle  and  higher  latitudes  are  lessened,  and 
the  climate  in  this  respect  resembles  a  marine  condi- 
tion; but  topography  and  the  conditions  of  local 
clouds  and  winds  are  here  important  controls.  The 
times  of  occurrence  of  the  maximum  and  minimum 
are  also  much  influenced  by  local  conditions.  Figure 
9  shows  the  diurnal  march  of  temperature  for  Paris 
(solid)  and  the  Eiffel  Tower  (broken)  in  January 
and  July.  It  will  be  noted  that  the  times  of  maxi- 
mum and  minimum  are  retarded  on  the  Eiffel  Tower, 
and  that  the  range  is  less  than  at  the  earth's  surface. 
These  are  characteristics  of  mountain  climates.  Ele- 
vated, well-enclosed  valleys,  with  strong  sunshine, 
often  resemble  continental  conditions  of  large  tem- 
perature range;  and  plateaus,  as  compared  with 
mountains  at  the  same  altitude,  have  relatively  higher 
temperatures  and  larger  temperature  ranges.  Alti- 
tude tempers  the  heat  of  the  low  latitudes.  High 


CLIMATE 


mountain   peaks,   even  on  the  equator,   can  remain 
snow-covered  the  year  around;  the  plateau  of  south- 


J)l!            4*            81?         NOON          16*          20!?            0£rt 

40 

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8° 

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July 

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41?  81?          NOON  16*?  201? 

Paris  Eiffel  Tower 


24* 


FIG.  9.     DIURNAL  VARIATION  OF  TEMPERATURE  :  INFLUENCE  OF 
ALTITUDE 

ern  India,  at  6000  to  7000  ft.  above  sea-level,  always 
has  moderate  mean  temperature,  and  from  the  dense 


THE  CLASSIFICATION  OF  CLIMATES  81 

jungle  of  the  tropical  lowland  to  the  snowy  moun- 
tain top,  successive  zones  of  vegetation  are  en- 
countered. 

Nine-tenths  of  the  water  vapour  in  the  atmosphere 
are  below  21,000  feet.  Hence  mountains  are  im- 
portant vapour  barriers,  and  one  side  may  be  damp 
while  the  other  is  dry.  Curiously  mistaken  ideas  of 
distance  often  result  from  the  remarkable  clearness 
and  dryness  of  the  air  on  high  mountains.  No  gen- 
eral law  governs  the  variations  of  relative  humidity 
with  altitude,  but  on  the  mountains  of  Europe  the 
winter  is  the  driest  season,  and  the  summer  the 
dampest.  At  well-exposed  stations  there  is  a  rapid 
increase  in  the  vapour  content  soon  after  noon,  espe- 
cially in  summer.  The  same  is  true  of  cloudiness, 
which  is  often  greater  on  mountains  than  at  lower 
levels,  and  is  usually  at  a  maximum  in  summer,  while 
the  opposite  is  true  of  the  lowlands  in  the  temperate 
latitudes.  One  of  the  great  advantages  of  the  higher 
Alpine  valleys  in  winter  is  their  small  amount  of 
cloud.  This,  combined  with  their  low  wind  velocity 
and  strong  insolation,  makes  them  desirable  winter 
health  resorts.  Latitude,  altitude,  topography,  and 
winds  are  determining  factors  in  controlling  the 
cloudiness  on  mountains.  In  intermediate  latitudes 
there  is  a  seasonal  migration  of  the  level  of  maximum 
cloudiness,  and  of  maximum  relative  humidity,  from 
the  lowlands  in  winter  to  higher  altitudes  in  the 
warmer  months,  in  association  with  the  diurnal  con- 
vectional  movements  of  the  warmer  season.  Frequent 


52  CLIMATE 

rapid  local  changes  also  occur.  In  the  rare,  often 
dry,  air  of  mountains  and  plateaus,  evaporation  is 
rapid,  the  skin  dries  and  cracks,  and  thirst  is  increased. 
Rainfall  usually  increases  with  increasing  altitude 
up  to  a  certain  point,  beyond  which,  owing  to  the  loss 
of  water  vapour,  this  increase  stops.  The  zone  of 
maximum  rainfall  averages  about  6000  to  7000  feet 
in  altitude,  more  or  less,  in  intermediate  latitudes, 
being  lower  in  winter  and  higher  in  summer.  Moun- 
tains usually  have  a  rainy  and  a  drier  side;  the  con- 
trast between  the  two  is  greatest  when  a  prevailing 
damp  wind  crosses  the  mountain,  or  when  one  slope 
faces  seaward  and  the  other  landward.  When  the 
prevailing  winds  differ  little  in  dampness,  this  con- 
trast is  lessened,  and  there  may  then  be  a  very  close 
correspondence  between  the  rainfall  and  the  topo- 
graphic map  of  a  region.  Mountains  often  provoke 
rainfall,  and  local  "  islands,"  or,  better,  "  lakes,"  of 
heavier  precipitation  result.  Such  are  found  on  the 
mountains  of  the  Sahara,  and  of  other  deserts.  This 
local  precipitation  favours  the  growth  of  vegetation; 
small  streams  and  oases  are  found,  and  temporary 
camps,  or  more  permanent  settlements,  of  the  no- 
madic tribes  of  the  desert  are  there  established.  Well- 
marked  zones  of  vegetation  are  noted  under  such 
conditions,  as  in  the  transition  from  the  dry  Califor- 
nian  lowlands  up  through  the  deciduous,  and  then  the 
coniferous,  forests  of  the  Sierra  Nevada  to  the  snows 
on  the  summits.  Similarly,  the  high  plateaus  of 
southern  Utah  and  of  Arizona  are  high  enough  to  re- 


TEE  CLASSIFICATION  OF  CLIMATES  53 

ceive  fairly  abundant  rainfall,  while  the  lowlands  are 
arid. 

Mountains  resemble  marine  climates  in  having 
higher  wind  velocities  than  continental  lowlands; 
mountain  summits  have  a  nocturnal  maximum  of 
wind  velocity,  while  plateaus  usually  have  a  diurnal 
maximum.  Mountains  both  modify  the  general,  and 
give  rise  to  local,  winds.  Among  the  latter,  the  well- 
known  mountain  and  valley  winds  are  often  of  con- 
siderable hygienic  importance  in  their  control  of  the 
diurnal  period  of  humidity,  cloudiness,  and  rainfall, 
the  ascending  wind  of  daytime  tending  to  give  clouds 
and  rain  aloft,  while  the  opposite  conditions  prevail 
at  night.  The  high  temperature  and  dryness  of  the 
foelin,  which  is  of  immense  benefit  to  man  by  reason 
of  its  melting  and  evaporating  powers,  although  of- 
ten enervating  and  depressing,  result  from  the  fact  of 
a  descent  of  the  air  from  a  mountain  slope  or  summit. 
The  bora,  with  its  cold  gust,  is  a  wind  in  whose  de- 
velopment a  mountain  or  plateau  is  essential.  And 
the  mistral  of  southern  France  owes  some  of  its  cold 
to  radiation  over  the  interior  plateaus. 

Mountains  as  Climatic  Divides.  Veiy  different 
conditions  of  temperature,  pressure,  and  humidity 
may  be  found  on  the  opposite  sides  of  a  well-defined 
mountain  range,  because  such  a  range  interferes  with 
the  free  horizontal  interchange  of  the  lower  air. 
Mountain  ranges  which  trend  east  and  west,  like  the 
Alps  and  the  Himalayas,  separate  more  severe  from 
less  severe  climates ;  those  which  follow  a  coast-line,  as 


54  CLIMATE 

in  California,  Scandinavia,  or  eastern  Siberia,  separ- 
ate marine  from  continental.  Large  differences  of 
pressure  on  the  two  sides  may  be  equalised  by  a  flow 
of  air  across  the  mountain,  as  in  the  foehn. 


CHAPTER  III 

THE  CLASSIFICATION  OF  CLIMATES    (Continued) 

Supan's  Climatic  Provinces — Koppen's  Classification  of  Climates — 
Ravenstein's  Hygrothermal  Types — Classification  of  Rainfall 
Systems — Herbertson's  Natural  Geographical  Regions — Sum- 
mary and  Conclusions. 

Supans  Climatic  Provinces.  The  ordinary  classi- 
fication into  continental,  marine,  and  mountain  cli- 
mates is  too  general.  Some  scheme  of  classification  is 
needed  in  which  the  geographical  factor  plays  an  im- 
portant part,  and  which  recognises  the  types  of 
climate,  possessing  common  characteristics  of  tem- 
perature, rainfall,  and  winds,  that  occur  over  areas 
having  similar  topographic  conditions.  A  fairly  sim- 
ple scheme  of  this  kind  has  been  suggested  by  Supan, 
who  recognises  thirty-five  so-called  climatic  prov- 
inces, but  any  such  rigid  subdivision  is  obviously  sus- 
ceptible of  almost  infinite  modification.  Twenty-one 
of  these  provinces  are  in  the  eastern  hemisphere,  in- 
cluding- Polynesia ;  twelve  are  in  the  western,  and 
two  in  the  polar  zones.  The  description  of  these 
provinces  is  as  follows:1 

1.     Arctic    Province.     This     coincides    with    the 

1  Free  translation  of  original,  following  Bartholomew's  Atlas  of 
Meteorology,  p.  7. 

55 


56 


CLIMATE 


north  polar  cold  cap,  the  area  wherein  the  mean  tem- 
perature of  the  warmest  summer  month  is  never  over 
50°  F.,  and  within  which  trees  do  not  grow. 

2.  West  European  Province.  Mild  winters,  ow- 
ing to  influence  of  the  westerly  winds  and  Gulf 
Stream.  Yearly  temperature  range  under  59°  F. 


FIG.  10.    SUPAN'S  CLIMATIC  PROVINCES 


(15°  C.).  Plentiful  rainfall,  fairly  well  distributed 
throughout  the  year,  but  varying  in  quantity  owing 
to  great  diversity  of  land  contours.  The  climatic 
conditions  often  vary  in  short  distances,  and  hence  the 
region  can  be  divided  into  many  subdivisions. 

3.  East  European  Province.  Here  the  evidences 
of  a  land  climate  begin  to  be  observed ;  but  as  most  of 
the  region  is  a  plain,  differences  depend  mainly  on 
latitude.  The  rainfall  is  smaller  than  in  Province  2, 


CLASSIFICATION  OF  CLIMATES  57 

and  gradually  diminishes  towards  the  southeast,  and 
has  a  marked  summer  maximum. 

4.  West   Siberian   Province.     This  is   separated 
from  3  by  the  limit  of  the  positive  annual  isanomal- 
ous  lines,  which  practically  coincide  with  the  Urals. 
The  characteristic  peculiarities  of  3  are  found  here 
greatly  emphasised,  and  the  greater  variability  of 
temperature  is  to  be  noted. 

5.  East  Siberian  Province.     A  gradual  rising  of 
the  ground  is  found  east  of  the  Yenisei,  with  low 
plains  only  along  the  rivers.     The  winter  cold  pole 
is  here,  and  the  yearly  range  of  temperature  is  a 
maximum.     As  a  rule,  the  rainfall  is  small. 

6.  Kamchatkan    Province.     The    sea    diminishes 
the  temperature  extremes  noted  in  Province  5,  and 
much  rain  falls. 

7.  Sino-Japanese    Province.     On   the    continent, 
relatively  well-marked  winter  cold,  and  strong  peri- 
odical rains.     In  Japan,  these  peculiarities  are  less 
extreme. 

8.  Asiatic     Mountain     and     Plateau     Province. 
This    includes    all   the   lofty    plateaus   bounded   by 
mountain  ranges,  which  shield  it  on  every  side,  and 
so  render  it  very  dry.     The  great  height  makes  the 
winter  temperature  severe;  but  the  summer  heat  is 
great,  owing  to  the  continental  position.     The  daily, 
as  well  as  the  yearly,  range  of  temperature  is  very 
marked. 

9.  Aral  Province.     Dry,  low-lying  plain,  with  the 
greatest  rainfall  in  the  north  in  summer,  and  in  the 


58  CLIMATE 

south  in  winter.     The  plains  of  western  Turkestan 
have  severe  winters  and  very  hot  summers. 

10.  Indus    Province.     A    plain    remarkable    for 
great  dryness  and  heat. 

11.  Mediterranean    Province.     Very    varied    in 
climate,  owing  to  its  great  irregularity  of  outline, 
both  horizontal  and  vertical.     Mild,  except  on  high 
plateaus.     Winter  rains. 

12.  Saharan    Province.     Reaches    to    Mesopota- 
mia.    Region  of  dry,  north  winds,  and  probably  the 
one  receiving  least  rain.     Its  continental  position  and 
lack  of  vegetation  increase  the  heat  of  summer  ex- 
traordinarily; both  annual  and  daily  ranges  of  tem- 
perature are  considerable. 

13.  Tropical  African   Province.     Owing   to   the 
height  of  the  central  plateau,  the  heat  is  less  intense, 
but  it  is  very  great  on  the  narrow  coastal  plains. 
Tropical  rains  decreasing  towards  the  west. 

14.  Kalahari  Province.     Includes  all  the  almost 
rainless  region  of  southwest  Africa. 

15.  Cape  Province.     Sub-tropical. 

16.  Indo- Australian  Monsoon  Province.    Strong, 
periodical  rains  are  brought  with  the  southwest  and 
northwest  monsoons,  except  at  a  few  places  in  the 
archipelago.     The    temperature    is    fairly    uniform, 
despite  the  great  extent   of  the  province,   and   the 
yearly  range  is  very  small. 

17.  Inner  Australian  Province.     With  great  ex- 
tremes of  temperature.     Irregular  and  rare  rains. 

18.  Southwest  Australian  Province.  Sub-tropical. 


CLASSIFICATION  OF  CLIMATES  59 

19.  East  Australian  Province.     It  extends  to  the 
water-parting  and  includes  the  southeast  coast  and 
Tasmania.     Plentiful  and  fairly  regular  rains.  Mod- 
erate range  of  temperature. 

20.  New  Zealand  Province.     Probably  includes 
the  small  neighbouring  islands.     Mild  climate,  with 
fairly  regular  rains. 

21.  Tropical  Polynesian  Province.     Tropical  cli- 
mate, ameliorated  by  the  ocean,  so  that  mild  sum- 
mer weather  prevails  throughout  the  year.     On  the 
loftier  islands,  the  rain  is  abundant,  and  has  a  tropi- 
cal periodicity. 

22.  Hawaiian   Province.     Also    a    mild   climate, 
but  with  sub-tropical  rains. 

23.  Hudson  (North  Canadian)  Province.     Great 
extremes  of  temperature  and  little  precipitation. 

24.  Northwest  American  Coastal  Province.  Mild, 
equable,  rainy  climate. 

25.  Californian    Province.     Relatively    cool,    es- 
pecially   in    summer.      Marked    sub-tropical    rainy 
seasons. 

26.  North    American    Mountain    and    Plateau 
Province.     Great  yearly  and  daily  ranges.     Dry. 

27.  Atlantic    (East  North  American)    Province. 
Great  contrast  in  temperature  conditions  of  north 
and  south  in  winter.     Extreme  climate  even  on  the 
coast.     Plentiful  rains,  evenly  distributed  through- 
out the  year.     Great  variability. 

28.  West   Indian   Province.     This   also   includes 
the  southern  rim  of  North  America.     Equable  tern- 


60  CLIMATE 

perature.     Rain  at  all  seasons,  but  with  a  marked 
summer  maximum. 

29.  Tropical  Cordilleran  Province.     On  the  in- 
terior plateau,  perpetual  spring,  owing  to  consider- 
able height  above  sea-level.     In  Mexico  and  Central 
America,  marked  zenithal  rains;  in  South  America, 
more  regular  precipitation. 

30.  South  American  Tropical  Province.     Little 
that  is  certain  is  known  about  this  province,  which  in- 
cludes mountainous  regions  and  plains,  and  ought, 
therefore,  to  possess  considerable  variety  of  climate. 

31.  Peruvian   Province.     This   province   extends 
as  far  south  as  30°  S.,  and  so  includes  the  northern 
part  of  Chile.     Abnormally  cool.     Rainless. 

32.  North  Chilean  Province.     Sub-tropical. 

33.  South  Chilean  Province.     Equable  tempera- 
tures, with  cool  summers.     Extraordinarily  rainy. 

34.  Pampa    Province.     Range    of    temperature 
fairly    large,    especially    in    the    north.      Rain    not 
plentiful. 

35.  Antarctic  Province.    Resembles  the  Arctic,  so 
far  as  can  at  present  be  determined,  in  winter  cold 
but  differs  in  having  a  very  low  summer  temperature 
and  a  very  regular  distribution  of  pressure  and  winds. 

Fig.  10  showrs  the  geographical  distribution  of 
these  climatic  provinces. 

Koppens  Classification  of  Climates.  An  interest- 
ing classification  of  climates,  from  a  botanical  stand- 
point, is  that  proposed  by  Koppen.  This  rests  upon 
certain  critical  values  of  the  temperature  and  rain- 


CLASSIFICATION  OF  CLIMATES  61 

fall  of  the  warmest  or  coldest,  or  of  the  wettest  and 
driest  month.  The  plant  classification  proposed  by 
A.  de  Candolle  in  1874,  and  later  adopted  by  Drude, 
is  accepted.  This  is  a  division  into  five  principal 
biological  groups  under  the  control  of  temperature 
and  moisture,  as  follows: 

A.  Mcgatherms:  plants  which  need  continuously 
high  temperature  without  much  annual  range,  and 
also  abundant  moisture.     There  is  no  cool  season;  the 
temperature  of  the    coolest    month    is    over    64.5° 
(18°  C.) ,  and  there  is  at  least  one  month  of  heavy  rain. 
When  there  are  marked  dry  seasons,  the  principal  one 
comes  in  winter  and  spring.     In  parts  of  this  belt 
there  are  two  rainy  seasons.     In  this  belt  are  found 
the  lofty  tropical  forests  intertwined  with  vines  and 
creepers — sago,    betel,    pepper,    cacao,    bread-fruit, 
baobab,  coffee,  sugar-cane,  banana,  ginger,  and  so  on. 

B.  Xerophytes:  plants   which  like   dryness   and 
need  high  temperatures,  at  least  for  a  short  season. 
These  are  found  in  tropical  districts  which  have  a 
long  dry  season,  and  in  the  steppes  and  deserts  of  the 
tropics  and  of  the  warmer  parts  of  the  temperate 
zones.     They  are  adapted  in  various  ways  for  life  in 
a  dry  climate;  they  rest  during  the  dry  time,  and,  in 
extreme  cases,  where  rain  may  not  fall  for  years,  they 
survive  as  seeds.     The  vegetation  varies  with  the  soil. 
In  this  group  w^e  find  the  date,  mesquite,  acacia,  cac- 
tus, agave,  and  similar  plants. 

C.  Mesotherms:  need   moderate  heat    (59°-68°) 
and  a  moderate  amount  of  moisture;  some  require 


62  CLIMATE 

high  summer  temperatures;  others  shun  low  win- 
ter temperatures;  others  shun  the  dryness  which  of- 
ten accompanies  high  summer  temperatures.  These 
plants  inhabit  latitudes  between  22°  and  45°  N.  or 
40°  S.,  so  long  as  the  moisture  continues  sufficient. 
There  is  a  cool  season — coldest  month  below  64.5° 
(18°  C.) — and  a  hot  summer — warmest  month  over 
72°  (22°  C.), — or  a  mild  winter — coldest  month  over 
43°  (6°  C.)— or  both.  The  classic  Mediterranean 
climate  is  found  in  this  belt.  The  mesotherm  belt 
contains  the  tea,  mate,  rice,  cotton,  magnolia,  hickory, 
arbor  vite,  hemlock,  wheat,  corn,  olive,  fig,  grape, 
heath,  cinchona,  etc. 

D.  Mikrotherms:  need  less  heat,  lower  mean  an- 
nual temperature,  cooler  and  shorter  summers,  and 
colder  winters.     The  warmest  month  is  at  least  50° 
(10°  C.)  and  not  over  72°  (22°  C.)  ;  the  coldest  is  be- 
low 43°    (6°  C.),  writh  at  least  an  occasional  snow- 
cover  in  winter  and  sufficient  rainfall  in  the  warmer 
season.     Evergreen   and   deciduous   forests,    grains, 
and,  in  the  warmer  portions,  fruit  and  corn  are  found. 

E.  Hekistotherms:  plants  of  the  Arctic  zone,  be- 
yond the  limits  of  tree  growth  and  of  the  zone  of 
scrubby  Antarctic  vegetation.     These  need  the  least 
heat.     Mosses,  lichens,  and  similar  lowly  forms  are 
typical. 

A  simple  scheme  of  distribution  of  these  five  groups 
of  plants  may  first  be  developed  with  reference  to  an 
ideal  continent,  stretching  from  pole  to  pole,  with 
oceans  on  both  sides  and  without  mountains  (Fig. 


CLASSIFICATION  OF  CLIMATES 


63 


11).  Here  a  a  is  the  western  and  b  b  the  eastern 
coast.  The  approximate  latitudes  are  given  at  the 
margins.  The  groups  of  de  Candolle's  system  are 
arranged  as  shown,  if  the  xerophytes  are  limited  to 


60°  - 


60° 


FIG.   ii.      GENERAL   DISTRIBUTION  OF 
PLANT  ZONES 

the  deserts  and  steppes,  and  if  those  woody  plants 
of  the  megatherm  and  mesotherm  zones  which  are 
adapted  to  a  dry  climate  are  included  within  these 
zones.  The  typical  zonal  arrangement  is  interrupted 
in  latitudes  20°  to  50°  by  the  fact  that  the  arid  dis- 


64  CLIMATE 

trict  of  the  xerophytes  (B)  is  wedged  in  on  the  west 
coast  between  A  and  C.  Farther  east,  zone  B  broad- 
ens poleward,  cuts  through  the  middle  of  the  meso- 
therm  zone,  and  usually  ends  without  reaching  the 
east  coast. 


FIG.  12.     SCHEME  OF  CLIMATES 
AT  SEA- LEVEL 

The  five  principal  types  are  further  subdivided  un- 
til the  whole  number  of  climates  reaches  twenty-four. 
The  special  conditions  which  characterise  each  cli- 
mate are  carefully  determined,  and  each  sub-climate 
is  named  after  one  of  its  characteristic  plants  or  ani- 


CLASSIFICATION  OF  CLIMATES 


65 


mals;  or  after  some  distinctive  meteorological  pheno- 
menon; or,  again,  after  the  general  character  of  its 
vegetation.  Fig  12  gives  the  limits  of  the  different 


FIG.  13.  NAMES  OF  CLIMATES 
AT  SEA- LEVEL 

sub-climates,  and  also  the  characteristic  conditions  of 
temperature  and  precipitation.1      Fig.  13  gives  the 

1  Figures  are  degrees  Fahr.  C  =  coldest  month.  W  =  warmest 
month.  4  M  =  4  months,  dr.  1.2  in.  =  driest  month  rainfall  1.2  in- 
ches. D.  18°  and  D  36°  =  difference  between  extreme  months 
18°  and  36°.  q  =  quotient  obtained  by  dividing  the  amount  of 
rainfall  in  the  wettest  month  (in  mm.)  by  the  maximum  vapour- 
tension  (in  mm.)  at  the  mean  temperature  of  the  same  month,  an 
5 


66  CLIMATE 

scheme  of  the  sub-climates  for  the  lowlands,  with  their 
names.  Four  climates  which  do  not  occur  at  sea- 
level  are  here  lacking  (C7,  E3,  E4,  F).1  The  verti- 


Alti- 

tude 

m. 

4000 


3OOO 


Vertical  Distribution,  of  Climates 
Marine  Type  Continental  Type 


Alti- 
tude 


m. 


3000 


FIG.    14.    VERTICAL  DISTRIBUTION  OF  CLIMATES 

cal  distribution  of  these  climates,  much  simplified,  is 
shown  in  Fig  14.  The  descent  of  the  climatic  strata 
from  equator  to  higher  latitudes  is  shown  on  the  right 
for  the  continental,  and  on  the  left  for  the  marine  type, 
as  far  as  about  latitude  57°.  Climates  Cl  to  C4, 
and  Dl  and  D2,  have  large  temperature  ranges,  and 
are  therefore  lacking  at  the  equator  and  on  the  ocean ; 
while  C5  to  C7,  and  D3,  have  small  ranges,  and  are 
not  found  on  the  continents  in  higher  latitudes.  The 
general  control  of  pressure,  winds,  and  ocean  currents 
over  the  climatic  types  is  shown  in  the  two  following 
ideal  diagrams,  in  which  the  two  vertical  lines  indi- 
cate the  west  and  east  coasts  of  the  ideal  continent,, 
and  the  area  included  reaches  to  the  middle  of  the  ad- 
expression  which  combines  the  effect  of  rainfall  and  evaporating 
power,  r  — rain  probability  of  rainiest  month. 

1  C7,  High  savanna  climate;    E3,  Yak,  or  Pamir  climate;   E4, 
Chamois  or  high  alpine  climate;  F,  perpetual  frost,  without  life. 


CLASSIFICATION  OF  CLIMATES 


67 


jacent  ideal  oceans.  The  line  0°-0°  is  the  equator 
(Figs.  15  and  16).  The  short  arrows  give  the  wind 
direction  500-1000  metres  above  the  surface;  calms 
are  represented  by  the  sign  o  ;  the  long  broken  arrows 


FIG.  15.     PRESSURE  AND  WINDS  IN  JANUARY 

indicate  the  prevailing  surface  ocean  currents.  At  a  a 
there  is  a  rise  of  cold  water  from  beneath  the  surface 
of  the  ocean.  The  curving  lines  are  sea-level  isobars ; 
the  lower  pressures  are  shaded.  The  letters  and 


68 


CLIMATE 


boundaries,  drawn  in  short,  slanting  lines  in  Fig.  16 
indicate  the  climatic  districts  of  Fig.  11.  Fig.  15  is 
similar  to  Fig.  16,  as  far  as  these  climatic  districts  are 


FIG.  16.     PRESSURE  AND  WINDS  IN  JULY 

concerned.  Therefore  the  letters  and  boundaries 
are  omitted.  Fig.  IT  shows  the  geographical  distri- 
bution of  the  climatic  types  and  sub-types. 

Eavenstein's  Hygrotliermal  Types,     Recognising 


70  CLIMATE 

the  importance  of  relative  humidity  as  a  climatic 
factor  in  its  influence  upon  life,  upon  agriculture  and 
upon  industry,  and  basing  his  grouping  of  climates 
upon  certain  relations  between  temperature  and  rela- 
tive humidity,  Ravenstein  proposes  a  subdivision  of 
the  earth's  surface  into  sixteen  hygrothermal  climatic 
types.  The  general  characteristics  and  examples  of 
these  types  are  as  follows: 

1.  Hot  (73°  and  over)  and  very  damp  (humidity 
81%  or  more)  :  Batavia,  Cameroons,  Mombasa. 

2.  Hot  and  moderately  damp    (66-80%):  Ha- 
vana, Calcutta. 

3.  Hot   and    dry    (51-65%):    Bagdad,    Lahore, 
Khartum. 

4.  Hot  and  very  dry  (50%  or  less)  :  Disa,  Wadi 
Haifa,  Kuka. 

5.  Warm  (58°  to  72°)  and  very  damp:  Walfish 
Bay,  Arica. 

6.  Warm  and  moderately  damp:  Lisbon,  Rome, 
Damascus,  Tokio,  New  Orleans. 

7.  Warm  and  dry:  Cairo,  Algiers,  Kimberley. 

8.  Warm  and  very  dry:  Mexico,  Teheran. 

9.  Cool  (33°  to  57°)  and  very  damp:  Greenwich, 
Cochabamba. 

10.  Cool   and  moderately   damp:   Vienna,    Mel- 
bourne, Toronto,  Chicago. 

11.  Cool  and  dry:  Tashkent,  Simla,  Cheyenne. 

12.  Cool  and  very  dry:  Yarkand,  Denver. 

13.  Cold  (32°  or  less)  and  very  damp:  Ben  Nevis, 
Sagastyr,  Godthaab. 


CLASSIFICATION  OF  CLIMATES 


71 


14.  Cold  and  moderately  damp:  Tomsk,  Pike's 
Peak,  Polaris  House. 

15.  Cold  and  dry:   (No  example  given). 

16.  Cold  and  very  dry:  Pamir. 
Classification  of  Rainfall  Systems. — The  seasonal 

occurrence  of  rainfall  has  suggested  a  classification 
of  the  rainfall  systems  of  the  world  into  types.  While 
these  schemes  are  useful  in  climatological  study,  they 
are  hardly  to  be  considered  as  classifications  of  cli- 


FIG.  18.     HERBERTSON'S  MAJOR  NATURAL  REGIONS 

mate.  Miihry  *  gave  a  rigid  scheme  of  rainfall  types 
in  six  belts  for  each  hemisphere,  these  belts  being 
divided  by  latitude  lines ;  and  Koppen  has  prepared 
a  useful  map  of  the  hyetal  regions  of  the  world,  based 
on  the  seasonal  distribution  of  rainfall  types.2 

1  A.    Miihry:    Klimatographische    Uebersicht   der  Erde,    Leipzig 
and   Heidelberg,    1862,   741-744.     Also:    Allgemeine   geographische 
Meteorologie,  1860,  145,  and  note  23,  199.     Containing  chart,  as 
well  as  the  scheme  of  rainfall  types. 

2  See  Atlas  of  Meteorology,  Plate  19. 


72  CLIMATE 

Herbertson  s  Natural  Geographical  Regions. — A 
scheme  of  "  natural  geographical  regions  "  has  been 
suggested  by  Herbertson,1  the  basis  of  classifica- 
tion being  a  certain  unity  of  temperature,  rainfall 
seasons,  configuration  and  vegetation  (Fig.  18). 

The  different  types  of  natural  regions  recur  in 
fairly  systematic  order  on  the  different  continents, 
being  chiefly  controlled  by  marine  and  continental  in- 
fluences, and  each  type,  wherever  found,  has  certain 
similar  general  relations  to  human  life  and  develop- 
ment, as  well  as  to  animals  and  plants.  The  types 
are  as  follows: 

1.  Polar,    (a)    Lowlands    (Tundra   type)  ;    (b) 
Highlands  (Icetcap  type). 

2.  The    cool    temperate    regions,      (a)    Western 
margin   (West  European  type)  ;   (b)   Eastern  mar- 
gin (Quebec  type)  ;  (c)  Interior  lowlands  (Siberian 
type);   (d)   Interior  mountain  area  (Altai  type). 

3.  The  warm  temperate  regions,      (a)    Western 
margin    with    winter    rains    ( Mediterranean    type) ; 
(b)  The  eastern  margin,  with  summer  rains  (China 
type);  (c)  The  interior  lowlands  (Turan  type)  ;  (d) 
Plateau  (Iran  type). 

4.  (a)   The  west  tropical  deserts  (Sahara  type); 
(b)  East  tropical  lands  (Monsoon  type)  ;  (c)  Inter- 
tropical  table-lands  (Sudan  type). 

1  A.  J.  Herbertson:  "The  Major  Natural  Regions:  An  Essay  in 
Systematic  Geography."  Geogr.  Journ.  xxv.,  1905,  300-309.  A 
revised  chart  has  been  published  in  Herbertson's  The  Senior 
Geography,  Oxford,  1907.  (The  Oxford  Geographies,  Vol.  III.) 


CLASSIFICATION  OF  CLIMATES  73 

5.  Lofty  tropical  or  sub-tropical  mountains  (Tib- 
etan type) . 

6.  Equatorial  lowlands   (Amazon  type). 

Summary  and  Conclusions.  The  broad  classifica- 
tion of  climates  into  the  three  general  groups  of 
marine,  continental,  and  mountain,  with  the  subor- 
dinate divisions  of  desert,  littoral,  and  monsoon,  is 
convenient  for  purposes  of  summarising  the  interac- 
tion of  the  climatic  elements  under  the  controls  of 
land,  water,  and  altitude.  But  in  any  detailed  study, 
some  scheme  of  classification  is  needed  in  which  simi- 
lar climates  in  different  parts  of  the  world  are 
grouped  together,  and  in  which  their  geographic  dis- 
tribution receives  particular  consideration.  It  is  ob- 
vious from  the  preceding  paragraphs  that  an  almost 
infinite  number  of  classifications  might  be  proposed; 
for  we  may  take  as  the  basis  of  subdivision  either  the 
special  conditions  of  one  climatic  element,  as,  for  ex- 
ample, the  same  mean  annual  temperature,  or  mean 
annual  range  of  temperature,  or  the  same  rainfall,  or 
rainy  seasons,  or  humidity,  and  so  on.  Or  again, 
similar  conditions  of  the  combination  of  two  or  more 
elements  of  climate  may  be  made  the  basis  of  classifi- 
cation. Or  we  may  take  a  botanical,  or  a  zoological 
basis.  Of  the  classifications  which  have  been  pro- 
posed, special  reference  is  here  made  to  those  of 
Supan,  Koppen,  and  Herbertson.  That  of  Supan, 
taken  as  a  whole,  gives  a  rational,  simple,  and  satis- 
factory scheme  of  grouping,  whose  frequent  use  in 
climatic  descriptions  would  tend  toward  system,  sim- 


74  CLIMATE 

plicity,  and  facility  of  comparison.  It  emphasises 
the  essentials  of  each  climate,  and  serves  to  impress 
these  essentials  upon  the  mind  by  means  of  the  com- 
pact, well-considered  summary  which  is  given  in  the 
case  of  each  province  described.  Obviously,  no  clas- 
sification of  climates  which  is  at  all  complete  can  ap- 
proach the  simplicity  of  the  ordinary  classification  of 
the  zones. 

Koppen's  admirable  scheme  of  subdividing  climates, 
with  the  emphasis  on  the  botanical  side,  is  perhaps 
better  adapted  to  the  use  of  students  of  plant  geogra- 
phy than  of  general  climatology.  But  it  has  the 
great  merit  of  recognising  the  existing  differences  of 
climate  between  east  and  west  coasts,  and  between 
coasts  and  interiors.  The  co-ordination  of  districts 
of  vegetation  and  of  climate,  which  this  scheme  so 
strikingly  emphasises,  is  a  noteworthy  fact  in  clima- 
tology. The  subdivision  could  obviously  be  continued 
almost  indefinitely. 

Herbertson's  classification  of  the  natural  geo- 
graphical regions  is,  on  the  whole,  not  very  unlike  that 
adopted  in  Supan's  climatic  provinces,  but  is  less  com- 
plete. It  is  obvious  that  no  scheme  of  subdivision 
of  this  kind  can  be  regarded  as  being  rigid  or  as  sat- 
isfying all  students  of  questions  of  distribution. 
Nevertheless,  some  general  grouping  of  climatic  re- 
gions with  reference  to  similar  features  of  tempera- 
ture and  rainfall  and  configuration,  is  a  distinct  help 
in  most  geographical  studies.  The  larger  types 
naturally  recur  on  the  several  continents,  in  a  fairly 


CLASSIFICATION  OF  CLIMATES  75 

systematic  fashion.  It  results  from  this  fact  that 
there  is  a  recurrence,  in  a  large  way,  of  somewhat 
similar  conditions  of  life.  This  is  a  particularly  help- 
ful consideration  in  investigations  of  the  economic 
and  political  history  of  mankind.  The  chief  pecul- 
iarities of  the  important  types  can  be  readily  learned ; 
the  special  variations  in  individual  areas  may  be  in- 
vestigated for  each  case  by  itself. 

Ravenstein's  hygrothermal  types  rest  upon  unsatis- 
factory data,  and  regions  of  very  different  climatic 
conditions  are  grouped  together  because  they  happen 
to  have  the  same  mean  annual  temperature  and  rela- 
tive humidity. 


CHAPTER  IV 

THE   CHARACTERISTICS   OF   THE   ZONES:    I.— THE 

TROPICS 

General:  Climate  and  Weather — Temperature — The  Seasons — 
Physiological  Effects  of  Heat  and  Humidity — Pressure — Winds 
and  Rainfall — Land  and  Sea  Breezes — Thunderstorms — Cloudi- 
ness— Intensity  of  Skylight  and  Twilight — Climatic  Subdivi- 
sions:—I.  The  Equatorial  Belt.— II.  Trade  Wind  Belts.— III. 
Monsoon  Belts. — IV.  Mountain  Climate. 

General:  Climate  and  Weather.  The  so-called 
"  torrid  zone "  has  been  variously  bounded.  Its 
limits  have  been  set  at  the  tropics  (lat.  231/4°)  ;  at  the 
mean  annual  isotherms  of  68°,  which  also  correspond 
closely  with  the  poleward  extension  of  palms;  and  at 
the  polar  margins  of  the  trade  winds.  The  dominant 
characteristic  of  this  great  belt,  embracing  but  a  little 
less  than  one-half  of  the  earth's  surface,  is  the  re- 
markable simplicity  and  uniformity  of  its  climatic 
features.  This  simplicity  is  reflected  in  the  striking 
regularity  in  the  recurrence  of  the  ordinary  weather 
phenomena.  The  tropics  lack  the  proverbial  uncer- 
tainty and  changeableness  which  characterise  the 
weather  of  the  higher  latitudes.  In  the  torrid  zone, 
weather  and  climate  are  essentially  synonymous 
terms.  Periodic  phenomena,  depending  upon  the 
daily  and  annual  march  of  the  sun,  are  dominant. 
Non-periodic  weather  changes  are  wholly  subordi- 

76 


CHARACTERISTICS  OF  ZONES— TROPICS       77 

nate.  The  succession  of  daily  weather  changes  is  even 
more  regular,  and  the  distribution  of  the  climatic  ele- 
ments is  even  more  uniform  over  the  tropical  oceans 
than  over  the  lands.  In  special  regions  only,  and  at 
special  seasons,  is  the  regular  sequence  of  weather 
temporarily  interrupted  by  an  occasional  tropical 
cyclone.  These  cyclones,  although  comparatively  in- 
frequent, are  notable  features  of  the  climate  of  the 
areas  in  which  they  occur.  Generally  bringing  very 
heavy  rains,  and  thus  locally  increasing  the  total  an- 
nual precipitation  by  a  considerable  amount,  they  yet 
cause  no  marked  temperature  changes  such  as  those 
which  are  the  common  accompaniments  of  extra- 
tropical  cyclones.  The  devastation  produced  by  one 
of  these  storms  often  affects  the  economic  condition 
of  the  people  in  the  district  of  its  occurrence  for  many 
years. 

Temperature.  The  sun  is  always  well  up  in  the 
sky.  The  length  of  day  and  night  varies  little. 
Hence  the  mean  temperature  is  high,  it  is  very  uni- 
form over  the  whole  zone,  and  there  is  little  variation 
during  the  year.  The  mean  annual  isotherm  of  68° 
is  a  rational  limit  at  the  polar  margins  of  the  zone, 
and  the  mean  annual  isotherm  of  80°  encloses  the 
greater  portion  of  the  land  areas,  as  well  as  much  of 
the  tropical  oceans.  The  isotherms  are  thus  far 
apart.  The  warmest  latitude  circle  for  the  year  is 
not  the  equator,  but  latitude  10°  north.  The  highest 
mean  annual  temperatures,  shown  by  the  isotherm 
of  85°,  are  in  central  Africa,  in  India,  the  north  of 


78  CLIMATE 

Australia  and  Central  America,  but,  with  the  excep- 
tion of  the  first,  these  areas  are  small.  Massowah,  on 
the  Red  Sea,  has  an  annual  mean  of  over  86°.  The 
temperatures  average  highest  where  there  is  little 
rain,  and  not  in  the  belt  of  heavy  equatorial  rains, 
where  the  clouds  afford  some  protection  from  the 
sun's  rays.  In  June,  July,  and  August  there  are 
large  districts  in  the  south  of  Asia,  and  in  northern 
Africa,  with  temperatures  over  90°.  Winds  blowing 
out  from  these  heated  deserts  are  uncomfortably  hot 
and  dusty. 

Over  nearly  all  of  the  zone  the  mean  range  of  tem- 
perature is  less  than  10°,  and  over  much  of  it,  especi- 
ally the  oceans,  it  is  less  than  5°.  At  Equatorville, 
in  the  interior  of  Africa,  on  the  Congo,  the  mean 
annual  range  is  only  a  little  over  2°;  at  Iquitos  (lat. 
3.7°  S.),  in  Peru,  it  is  4.3°.  Even  near  the  margins 
of  the  zone,  where  the  seasonal  differences  are  great- 
est, the  ranges  are  less  than  25°,  as  at  Calcutta,  Hong 
Kong,  Rio  de  Janeiro  and  Khartum.  The  mean 
daily  range  is  usually  larger  than  the  mean  annual. 
Thus  at  Equatorville  the  former  is  about  14.5°.  It 
has  been  well  said  that  "  night  is  the  winter  of  the 
tropics."  The  differences  between  the  maximum  and 
minimum  temperatures  of  the  year  near  the  equator 
are  not  much  greater  than  the  daily  range.  Over  an 
area  covering  parts  of  the  Pacific  and  Indian  Oceans, 
from  Arabia  to  the  Caroline  Islands  and  from  Zan- 
zibar to  New  Guinea,  as  well  as  on  the  Guiana  coast, 


CHARACTERISTICS   OF  ZONES— TROPICS       79 

the  minimum  temperatures  do  not  normally  fall  be- 
low 68°,  and  over  much  of  the  torrid  zone  as  a  whole 
they  do  not  fall  below  59°.  Towards  the  margins  of 
the  zone,  however,  the  minima  on  the  continents  fall 
to,  or  even  below,  32°.  Maxima  of  115°,  and  even  over 
120°  (122°),  occur  over  the  deserts  of  northern 
Africa.  A  district  where  the  mean  maxima  exceed 
113°  extends  from  the  western  Sahara  to  northwest- 
ern India,  and  over  central  Australia.  Near  the 
equator  the  maxima  are  therefore  not  as  high  as  those 
in  many  so-called  "  temperate "  climates.  The 
greater  portion  of  the  torrid  zone  is  a  water  surface, 
and  marine  conditions  are  therefore  typical  for  most 
of  it.  These  tropical  oceans  show  remarkably  small 
variations  in  temperature.  The  Challenger  re- 
sults showed  a  daily  range  of  hardly  0.7°  in  the  sur- 
face water  temperature  on  the  equator,  and  Schott  de- 
termined the  annual  range  as  4.1°  on  the  equator;  4.3° 
at  latitude  10°,  and  6.5°  at  latitude  20°.  It  has  been 
clearly  pointed  out  by  Hann  that  the  uniform  dis- 
tribution of  temperature  throughout  the  year — the 
dominant  feature  of  the  tropics — results  not  only 
from  (1)  the  small  variation  in  insolation  and  in  the 
length  of  the  day;  but  also  (2)  from  the  great  extent 
of  the  zone,  which  makes  it  impossible  for  cold  winds 
from  higher  latitudes  to  penetrate  into  the  lower  lati- 
tudes; (3)  the  oblique  course  of  the  trades,  which  are 
well  warmed  on  their  indirect  road  towards  the  equa- 
tor; (4)  the  slight  nocturnal  cooling,  where  the  air 


80  CLIMATE 

is  damp  and  vapour  is  readily  condensed;  and  (5)  the 
great  extent  of  the  tropical  oceans,  which  gives  so 
much  of  the  zone  a  marine  climate. 

The  Seasons.  In  a  true  tropical  climate,  seasons, 
in  the  temperate  zone  sense,  do  not  exist.  The  varia- 
tions in  temperature  throughout  the  year  are  so  slight 
that  the  seasons  are  not  classified  according  to  tem- 
perature, but  depend  on  rainfall  and  the  prevailing 
winds.  The  life  of  animals  and  plants  in  the  tropics, 
and  of  man  himself,  is  regulated  very  largely,  in  some 
cases  almost  wholly,  by  rainfall.  Agriculture  pros- 
pers, or  fails,  according  to  the  sufficiency  and  punct- 
ual appearance  of  the  rains.  After  a  long  dry  season, 
when  the  rains  come,  there  is  an  extraordinarily 
sudden  awakening  of  the  parched  and  dusty  vegeta- 
tion. Where,  on  the  other  hand,  there  is  abundant 
moisture  throughout  the  year,  a  tree  may  at  the  same 
time  be  carrying  buds,  blossoms,  and  ripe  fruit. 
Vegetation  under  these  conditions  has  been  well  called 
non-periodic.  Although  the  tropical  rainy  season  is 
characteristically  associated  with  a  vertical  sun  (i.  e., 
summer),  that  season  is  not  necessarily  the  hottest 
time  of  the  year.  The  temperature  is  usually  some- 
what lower  under  the  clouds.  The  rainy  season  often 
goes  by  the  name  of  winter  for  this  reason,  and  also 
because  the  weather  is  dull.  The  time  of  the  maxi- 
mum temperature  is  also  controlled  by  the  rainy  sea- 
son. Towards  the  margins  of  the  zone,  with  increas- 
ing annual  ranges  of  temperature,  seasons  in  the  ex- 
tra-tropical sense  gradually  appear. 


CHARACTERISTICS  OF  ZONES— TROPICS       81 

Physiological  Effects  of  Heat  and  Humidity. 
Tropical  monotony  of  heat  is  associated  with  high 
relative  humidity,  except  over  deserts  and  in  diy  sea- 
sons. The  air  is  therefore  muggy  and  oppressive. 
The  high  temperatures  are  disagreeable  and  hard  to 
bear.  The  "  hot-house  air  "  has  an  enervating  effect. 
Energetic  physical  and  mental  action  are  often  diffi- 
cult, or  even  impossible.  The  tonic  effect  of  a  cold 
winter  is  lacking.  The  most  humid  districts  in  the 
tropics  are  the  least  desirable  for  persons  coming  from 
higher  latitudes;  the  driest  are  the  healthiest.  Tli2 
most  energetic  natives  are  the  desert-dwellers.  The 
monotonously  enervating  heat  of  the  humid  tropics 
weakens,  so  that  man  becomes  sensitive  to  slight  tem- 
perature changes.  A  fall  of  temperature  to  within 
a  few  degrees  of  70°  seems  to  some  tropical  natives 
almost  unbearably  cold,  and  certain  African  tribes 
sleep  on  clay  banks  heated  inside  by  fires,  although 
the  mean  temperature  of  the  coldest  month  is  over 
70°.  In  drier  climates  such  changes  are  more  easily 
borne.  The  intensity  of  direct  insolation,  as  well  as 
of  radiation  from  the  earth's  surface,  may  produce 
sunstroke  and  heat  prostration.  "Beware  of  the 
sun  "  is  a  good  rule  in  the  tropics. 

Pressure.  The  uniform  temperature  distribution 
in  the  tropics  involves  uniform  pressure  distribution. 
Pressure  gradients  are  weak.  The  annual  fluctuations 
are  slight,  even  on  the  continents.  The  diurnal  varia- 
tion of  the  barometer  is  so  regular  and  so  marked 
that,  as  von  Humboldt  said,  the  time  of  day  can  be 


82  CLIMATE 

told  within  about  fifteen  minutes  if  the  reading  of  the 
barometer  be  known.  Even  severe  thunderstorms  do 
not  overcome  the  regular  diurnal  march  of  the  press- 
ure, but  the  approach  of  tropical  cyclones  can  be 
foretold  by  the  pressure  changes. 

Winds  and  Rainfall.  Within  the  tropics,  there  are 
both  heavy  rains  and  large  districts  of  very  deficient 
precipitation.  Along  the  barometric  equator,  where 
the  pressure  gradients  are  weakest,  is  the  equatorial 
belt  of  calms,  variable  winds  and  rains — the  dol- 
drums. This  belt,  with  its  actively  ascending,  damp, 
hot  air,  offers  exceptionally  favourable  conditions  for 
abundant  rainfall,  and  belongs  among  the  rainiest 
regions  of  the  world,  averaging  probably  about  one 
hundred  inches.  The  rainfall  is  so  heavy  that  the 
salinity  of  the  surface  waters  of  the  oceans  is  actu- 
ally less  than  in  the  latitudes  of  the  trades.  The 
sky  is  prevailingly  cloudy,  especially  in  the  early 
afternoon  hours ;  the  air  is  hot  and  oppressive ;  heavy 
showers  and  thunderstorms  are  frequent,  chiefly  in 
the  afternoon  and  evening — conditions  not  very  un- 
like those  which  exist  during  certain  spells  of  sum- 
mer weather  in  the  north  temperate  zone.  There  are 
the  dense  tropical  forests  of  the  Amazon  and  of  equa- 
torial Africa.  There  frost  and  drought  need  not  be 
feared.  This  belt  of  calms  and  rains,  of  variable 
width  and  rather  indefinite  limits,  shifts  north  and 
south  of  the  equator  after  the  sun.  It  is  dreaded  by 
seamen  because  sailing  vessels  are  apt  to  have  long 
delays  in  crossing  it.  The  calm  belt  is  generally 


CHARACTERISTICS   OF  ZONES— TROPICS       83 

somewhat  narrower  than  the  belt  of  rains,  the  warm 
ascending  air  being  carried  north  and  south,  and  giv- 
ing precipitation  beyond  the  limits  of  the  calm  zone. 
In  striking  contrast  are  the  easterly  trade  winds, 
blowing  between  the  tropical  high  pressure  belts  and 
the  equatorial  belt  of  low  pressure,  and  supplying  to 
the  doldrum  belt  a  constant  flow  of  warm  air  which 
already  contains  a  large  amount  of  water  vapour, 
evaporated  from  the  oceans  by  the  trades,  and  needs 
only  a  moderate  cooling  in  order  to  give  abundant 
rainfall.  Of  great  regularity,  embracing  about  one- 
half  of  the  earth's  surface,  and  adding  greatly  to  the 
uniformity  of  tropical  climates,  the  trades  have  long 
been  favourite  sailing  routes  because  of  the  steadi- 
ness of  their  winds,  the  infrequency  of  storms,  the 
brightness  of  their  skies,  and  the  freshness  of  the  air, 
all  of  which  are  in  pleasing  contrast  with  the  muggy 
and  oppressive  calms  of  the  doldrums.  The  most  de- 
sirable house-sites  in  the  tropics  are  very  commonly 
on  the  top  of  some  elevation,  exposed  to  the  trade 
wind.  The  trades  are  subject  to  many  variations. 
Their  northern  and  southern  margins  shift  north  and 
south  after  the  sun;  at  certain  seasons  they  are 
interrupted,  often  over  wide  areas  near  their  equator- 
ward  margins,  by  the  migrating  belt  of  equa- 
torial rains  and  by  monsoons;  near  lands,  they 
are  often  interfered  with  by  land  and  sea  breezes; 
in  certain  regions,  they  are  invaded  by  violent 
cyclonic  storms.  The  trades,  except  where  they  blow 
onto  windward  coasts,  or  over  mountains,  are  natu- 


84  CLIMATE 

rally  drying  winds,  for  they  blow  from  higher  to  lower 
latitudes.  Some  facts  seem  to  show  that  there  is  a 
descending  component  in  the  trades.  They  cause  the 
deserts  of  northern  and  southern  Africa,  eastern  Asia, 
Australia,  and  southern  South  America.  Over  the 
oceans,  the  only  rains  in  the  trade  wind  belts  are  in 
the  form  of  passing  showers. 

The  monsoons  on  the  southern  and  eastern  coasts 
of  Asia  are  the  best  known  winds  of  their  class.  In 
the  northern  summer,  the  south-west  monsoon,  warm 
and  sultry,  blows  over  the  latitudes  from  about  10° 
north  to  and  beyond  the  northern  tropic,  between 
Africa  and  the  Philippines,  giving  rains  over  India, 
the  East  Indian  Archipelago,  and  the  east  coasts  of 
China.  These  winds  reach  a  storm  velocity  over  the 
Arabian  sea.  In  winter,  the  north-east  monsoon,  the 
normal,  cold-season,  continental  outflow  from  Asia, 
combined  with  the  north-east  trade,  generally  cool  and 
dry,  covers  the  same  district,  extending  as  far  north 
as  latitude  30°.  Crossing  the  equator,  these  winds 
reach  northern  Australia,  and  the  western  islands  of 
the  South  Pacific,  as  a  north-west  rainy  monsoon, 
while  this  region  in  the  opposite  season  has  the  normal 
south-east  trade.  Other  monsoons  are  found 
in  the  Gulf  of  Guinea  and  in  equatorial  Africa. 
Wherever  they  occur,  they  control  the  seasonal 
changes. 

The  most  important  climatic  phenomenon  of  the 
year  in  the  tropics  is  the  rainy  season.  Tropical 
rains  are,  in  the  main,  summer  rains,  i.  e.,  they  follow, 


CHARACTERISTICS   OF  ZONES— TROPICS       85 

as  a  general  rule,  soon  after  the  "  vertical  sun,"  l  the 
rainy  season  coming  when  the  normal  trade  gives  way 
to  the  equatorial  belt  of  rains,  or  when  the  summer 
monsoon  sets  in.  There  are,  however,  many  cases 
of  a  rainy  season  when  the  sun  is  low,  especially  on 
windward  coasts  in  the  trades.  Tropical  rains  come 
usually  in  the  form  of  heavy  downpours  and  with 
a  well-marked  diurnal  period,  the  maximum  varying 
with  the  locality  between  noon  and  midnight.  The 
conditions  at  Calcutta,  as  shown  in  the  accompany- 
ing data,  are  fairly  typical.2 

DIURNAL   DISTRIBUTION    OF    RAINFALL   AT    CALCUTTA. 


12 

P.M.  2     A. 

M. 

50 

12  M.  2     P.M. 

Ill 

2-4  A. 

M. 

71 

2-4  P.M 

116 

4-6  A. 

M. 

65 

4-6  P.M. 

120 

6-8  A. 

M. 

71 

6-8  P.M. 

128 

8-10  A. 

M. 

58 

8-10  P.M. 

73 

10A.M.—  12 

M. 

92 

10  P.M.  12  P.M. 

45 

Local  influences  are,  however,  very  important,  and 
in  many  places  night  rainfall  maxima  are  found. 

The  tropical  rainy  season  is  therefore  not  to  be 
thought  of  as  a  period  of  continuous  rains,  falling 
steadily  day  and  night  for  week  after  week.  The 
mornings  are  often  fine,  with  clean  air,  well  washed 
by  the  rains  of  the  preceding  afternoon  or  night. 
Woeikof 's  detailed  studies  of  tropical  rainfalls,  as  a 
whole,  lead  him  to  the  conclusion  that  (1)  the  inten- 
sity of  tropical  rains  averages  higher  than  in  middle 

1  It  will  be  remembered  that  at  all  places  within  the  tropics  the 
sun  is  vertical  twice  in  the  year. 

2  Seven  year  record ;  expressed  in  thousandths  of  the  daily  mean. 


86  CLIMATE 

latitudes,  but  the  difference  is  not  great;  (2)  the 
heaviest  short  downpours  have,  so  far  as  observation 
now  goes,  occurred  in  middle  latitudes;  (3)  general, 
moderate  rainfalls  lasting  continuously  for  many 
hours,  which  are  common  in  the  temperate  zones,  are 
known  in  many  parts  of  the  tropics  and  have  even 
been  given  special  names ;  ( 4 )  the  heaviest  daily  rain- 
falls have  been  noted  outside  the  tropics,  as  at  Cherra- 
punji,  for  example;  and  (5)  it  is  likely  that  the  most 
intense  rains  in  the  tropics  fall  during  large  tropical 
cyclones. 

Land  and  Sea  Breezes.  The  sea  breeze  is  an  im- 
portant climatic  feature  on  many  tropical  coasts. 
With  its  regular  occurrence,  and  its  cool,  clean  air, 
it  serves  to  make  many  districts  habitable  for  white 
settlers,  and  has  deservedly  won  the  name  of  "  the 
doctor."  On  not  a  few  coasts,  the  sea  breeze  is  a 
true  prevailing  wind.  The  location  of  dwellings  is 
often  determined  by  the  exposure  of  a  site  to  the  sea 
breeze.  For  this  reason,  many  native  villages  are  put 
as  near  the  sea  as  possible.  The  houses  of  well-to-do 
foreigners  often  occupy  the  healthiest  and  most  de- 
sirable locations,  where  the  sea  breeze  has  a  free  en- 
trance, while  the  poorer  native  classes  live  in  the  lower, 
less  exposed  and  less  desirable  places.  A  social 
stratification  is  thus  determined  by  the  sea  breeze. 

Thunderstorms.  Local  thunderstorms  are  fre- 
quent in  the  humid  portions  of  the  tropics.  They 
have  a  marked  diurnal  periodicity;  find  their  best 
opportunity  in  the  equatorial  belt  of  weak  pressure 


CHARACTERISTICS   OF  ZONES— TROPICS       87 

gradients  and  high  temperature,  and  are  commonly 
associated  with  the  rainy  season,  being  most  common 
at  the  beginning  and  end  of  the  regular  rains.  In 
many  places,  thunderstorms  occur  daily  throughout 
their  season,  with  extraordinary  regularity  and  great 
intensity.  Lightning  is,  however,  reported  as  very 
seldom  doing  any  damage.  Attention  has  been 
called  to  the  fact  that  the  frequent  electrical  dis- 
charges cause  the  rain  wrater  to  be  relatively  rich  in 
nitric  acid.  This  condition,  together  with  the  carbon 
dioxide  in  the  rain  water  and  the  high  temperature 
of  the  same,  promotes  active  and  deep  rock  decom- 
position. In  higher  latitudes,  where  the  ground  may 
be  frozen  part  of  the  year,  and  where  the  decompos- 
ing action  of  rain  water  is  less,  there  is  less  of  this 
effect.  In  northern  India,  hail-storms  of  great 
violence  occur,  and  persons  have  been  killed  by 
them. 

Cloudiness.  Taken  as  a  whole,  the  tropics  are  not 
favoured  with  such  clear  skies  as  is  often  supposed. 
Cloudiness  varies  about  as  does  the  rainfall.  The 
maximum  is  in  the  equatorial  belt  of  calms  and  rains, 
where  the  sky  is  always  more  or  less  cloudy.  The 
minimum  is  in  the  trade  latitudes,  where  fair  skies  as 
a  whole^  prevail.1  The  equatorial  cloud  belt  moves 
north  and  south  after  the  sun.  Wholly  clear  days 
are  very  rare  in  the  tropics  generally,  especially  near 

1  Supan,  Gt*undzuge  der  Physischen  Erdkunde,  3d  ed.,  1903,  Fig. 
13,  page  53,  gives  a  diagram  showing  the  distribution  of  rainfall 
and  cloudiness  (also  of  other  elements)  according  to  latitude. 


88  CLIMATE 

the  equator,  and  during  the  rainy  season  heavy  clouds 
usually  cover  the  sky. 

Tropical  clouds  and  rainfall,  as  a  whole,  repeat,  in 
an  exaggerated  form,  the  summer  conditions  of  much 
of  the  north  temperate  zone.  Broken  skies;  cumulus 
and  cumulo-nimbus  clouds;  heavy  showers  or  thun- 
derstorms— these  usually  characterise  the  rainy  sea- 
son. Skies  clear,  or  flecked  with  scattered  small 
cumuli,  are  typical  of  the  dry  season.  Wholly  over- 
cast, dull  days,  such  as  are  common  in  the  winter  of 
the  temperate  zone,  occur  frequently  only  on  tropical 
coasts  in  the  vicinity  of  cold  ocean  currents,  as  in 
Peru  and  on  parts  of  the  west  coast  of  Africa.  In 
these  same  regions  ocean  fogs  are  common. 

Intensity  of  Skylight  and  Twilight.  The  inten- 
sity of  the  light  from  tropical  skies  by  day  is  trying, 
even  almost  unbearable,  to  newcomers.  The  intense 
insolation,  together  with  the  reflection  from  the 
ground,  increases  the  general  dazzling  glare  under  a 
tropical  sun,  necessitating  protection  of  some  sort. 
The  far-famed  deep  blue  of  the  tropical  sky  is  much 
exaggerated.  During  much  of  the  time,  smoke  from 
forest  and  prairie  fires  (in  the  dry  season)  ;  dust  (in 
deserts),  and  water  vapour  give  the  sky  a  pale,  whit- 
ish appearance.  In  the  heart  of  the  trade  wind  belts 
at  sea,  the  sky  is  much  more  of  a  deep  blue.  The 
beauties  of  tropical  sunrise  and  sunset,  and  of  the 
tropical  night,  have,  however,  not  been  overrated. 
Twilight  within  the  tropics  is  shorter  than  in  higher 
latitudes,  but  the  coming  on  of  night  is  less  sudden 


CHARACTERISTICS   OF  ZONES—TROPICS       89 

than  is  generally  assumed.  Pechuel-Losche  and 
others  have  shown  that  it  is  possible,  on  the  Loango 
coast,  to  read  ordinary  print  twenty  to  thirty  minutes 
after  sunset. 

Climatic  Subdivisions.  The  rational  basis  for  a 
classification  of  the  larger  climatic  provinces  of  the 
torrid  zone  is  found  in  the  general  wind  systems  and 
in  their  control  over  rainfall.  Following  this  scheme 
there  are  these  subdivisions:  I.  The  equatorial  belt; 
II.  The  trade  wind  belts;  III.  The  monsoon  belts. 
In  each  of  these  subdivisions  there  are  modifications, 
due  to  ocean  and  continental  influences.  In  general 
both  seasonal  and  diurnal  phenomena  and  changes 
are  more  marked  in  continental  interiors  than  on  the 
oceans,  islands,  and  windward  coasts.  Further,  the 
effect  of  altitude  is  so  important  that  another  subdi- 
vision should  be  added  to  include  IV.  Mountain 
climates. 

I.  The  Equatorial  Belt.  Within  a  few  degrees 
of  the  equator,  and  when  not  interfered  with  by  other 
controls,  the  annual  curve  of  temperature  has  two 
maxima  following  the  two  zenithal  positions  of  the 
sun,  and  two  minima  at  about  the  time  of  the  solstices. 
This,  which  is  known  as  the  equatorial  type  of  annual 
march  of  temperature,  is  illustrated  in  the  data 
and  curves  for  the  interior  of  Africa,  Batavia,  and 
Jaluit.  (Fig.  19). 

The  greatest  range  is  shown  in  the  curve  for  the  in- 
terior of  Africa;  the  curve  for  Batavia  illustrates  in- 
sular conditions  with  less  range ;  and  the  oceanic  type, 


90 


CLIMATE 


for  Jaluit,  Marshall  Islands,  gives  the  least  range. 
At  Jaluit,  the  daily  maxima  for  the  entire  year  are 
between  88°  and  91.5°  and  the  daily  minima  between 
75°  and  77°.  This  double  maximum  is  not  a 
universal  phenomenon,  there  being  many  cases  where 
but  a  single  maximum  occurs,  as  will  be  seen 
later. 

TABLE    OF    MEAN    MONTHLY    TEMPERATURES    FOR    SELECTED 
TROPICAL    STATIONS  1 


I.  Equatorial  Type 

II.     Tropical  Type 

Conti- 

Insular 

Marine 

Continental 

Monsoon 

Insular 

nental 

Africa 
interior 

Batavia 

Jaluit, 
Marshall 
Islands 

Wadi 
Haifa 

Alice 
Springs 

Nagpur 

Hono- 
lulu 

Jame: 
town 

Lat. 

8.1°  N. 

6°11'S. 

5°  55'  N. 

21°  53'  N. 

23°  38'  S. 

21°  9'  N. 

21°  18'  N. 

15°  55 

Long. 

23.6°  E. 

106°  50'  E. 

169°  40'  E. 

31°20'E. 

133°  37'  E. 

79°11'E. 

157°  50'  N. 

5°  43' 

Altitude 

1837  ft. 

23  ft. 

10  ft. 

426  ft. 

1926  ft. 

1093  ft. 

49  ft. 

39  ft 

Jan. 

73.4° 

77.5° 

80.8° 

61.3° 

85.6° 

682° 

70.0° 

74.7C 

Feb. 

77.2° 

77.7° 

81.0° 

66.6° 

83.3° 

738° 

70.3° 

75.9C 

Mar. 

83.8° 

78.4° 

80.6° 

73.0° 

77.9° 

837° 

70.9° 

73.6C 

&E? 

85.3° 
83.7° 

79.3° 
79.5° 

80.4° 
80.4° 

81.0° 
87.1° 

68.5° 
60.6° 

90.3° 
94.3° 

72.9° 
74.3° 

75.0C 
68.9C 

June 

81.5° 

78.8° 

80.2° 

91.4° 

54.0° 

856° 

76.1° 

70.5e 

July 

78.4° 

78.3° 

80.2° 

93.4° 

51.8° 

80.1° 

77.2° 

71.8C 

Aug. 

75.7° 

78.6° 

80.4° 

91.6° 

59.4° 

80.2° 

77.5° 

69.4° 

Sept. 

77.7° 

79.3° 

80.4° 

87.1° 

66.6° 

804° 

77.2° 

67.6° 

Oct. 

78.1° 

79.5° 

80.8° 

83.1° 

73.4° 

78.6° 

76.5° 

65.7C 

Nov. 

75.7° 

79.0° 

80.8° 

71.4° 

79.7° 

723° 

73.8° 

67.8° 

Dec. 

72.9° 

78.1° 

80.6° 

64.8° 

82.8° 

66.7° 

71.4° 

71.8C 

Mean 

78.6° 

78.8° 

80.6° 

79.3° 

70.3° 

79.5° 

73.9° 

71.1° 

Range 

12.4° 

2° 

0.8° 

32.1° 

33.8° 

27.6° 

7.5 

10.2« 

1 

As  the  belt  of  rains  swings  back  and  forth  across 
the  equator  after  the  sun,  there  should  be  two  rainy 
seasons  with  the  sun  vertical,  and  two  dry  seasons 
when  the  sun  is  farthest  from  the  zenith,  and  while 


1  Given  to  nearest  tenth  of  a  degree  Fahr. 


CHARACTERISTICS   OF   ZONES— TROPICS       91 

the  trades  blow.  These  conditions  prevail  on  the 
equator,  and  as  far  north  and  south  of  the  equator 
(about  10°-12°)  as  sufficient  time  elapses  between 
the  two  zenithal  positions  of  the  sun  for  the  two  rainy 


FIG.  19.      ANNUAL  MARCH  OF  TEMPERATURE  :    EQUATORIAL  TYPE. 
A:   Africa,  interior.     B:  Batavia.     J:  Jaluit,  Marshall  Islands. 

seasons  to  be  distinguished  from  one  another.  In 
this  belt,  under  normal  conditions,  there  is,  therefore, 
no  dry  season  of  any  considerable  duration.  The 
double  rainy  season  is  clearly  seen  in  equatorial 


.1 

F 

M 

A 

M 

J 

J 

A 

S 

0. 

N. 

D. 

J. 

JOOOTHS 
250 

.^ 

/" 

200 

^S 

j 

150 

\ 

f 

- 

100 
50 

P.O. 

V 

s^ 

s 

^ 

- 

150 

. 

100 

«-• 

--—  —  ^ 

•""V 

^—  — 

—  — 

•^v 

^. 

50 

H. 

x^. 

*-*s* 

- 

200 

_—  * 

.  — 

. 

150 

r 

\ 

- 

100 
50 

_/ 

/ 

\ 

\ 

| 

„ 

0 

— 

v—  . 

•—«_ 

•» 

200 

'    X 

.. 

150 

X 

r  . 

100 

\ 

^*— 

^/ 

X 

'. 

50 

S.P. 

N^ 

^ 

^ 

^ 

^ 

/ 

200 

. 

150 

/\ 

. 

100 

«*» 

.^-* 

^ 

\ 

s~ 

——  • 

•*—  . 

^« 

50 

V. 

x^" 

—  ' 

. 

. 

—-** 

200 
150 
100 
50 

-^ 

SA 

' 

A 

\ 

V 

.  —  ' 

j 

^ 

V 

-' 

J. 

F. 

M. 

A. 

M 

J. 

J. 

A. 

s. 

0. 

N. 

D. 

J. 

FIG.  20.    ANNUAL  MARCH  OF  RAINFALL 
IN  THE  TROPICS 

S.  A:    South  Africa.     Q:  Quito.     S.    P: 

Sao  Paulo.     M:  Mexico.     H:  Hilo. 

P,  D;  Port  Darwin. 


CHARACTERISTICS  OF  ZONES— TROPICS       93 

Africa  and  in  parts  of  equatorial  South  America. 
The  maxima  lag  somewhat  behind  the  vertical  sun, 
coming  in  April  and  November,  and  are  unsymmetri- 
cally  developed,  the  first  maximum  being  the  principal 
one.  The  minima  are  also  unsymmetrically  devel- 
oped, and  the  so-called  "  dry  seasons  "  are  seldom 
wholly  rainless.  In  this  equatorial  belt,  the  annual 
range  of  rainfall  is  generally  below  20%  ;  in  the  west- 
ern portion  of  the  Malay  Archipelago  and  on  the 
upper  Amazon,  it  is  below  10%.  In  these  latitudes, 
therefore,  the  distribution  of  rainfall  is  not  unlike  that 
in  extra-tropical  latitudes  which  are  under  the  marine 
regime  of  rainfall,  there  being  precipitation  at  all 
seasons. 

This  rainfall  type  with  double  maxima  and  minima 
has  been  called  the  equatorial  type,  and  is  illustrated 
in  the  following  data  and  in  the  curves  for  south 
Africa  and  Quito.  (Fig.  20) . 

The  mean  annual  rainfall  at  Quito  is  42.12  inches. 
These  double  rainy  and  dry  seasons  are  easily  modi- 
fied by  other  conditions,  as  by  the  monsoons  of  the 
Indo-Australian  area,  for  example,  so  there  is  no 
rigid  belt  of  equatorial  rains  extending  around  the 
world.  In  South  America,  east  of  the  Andes,  the 
distinction  between  rainy  and  dry  seasons  is  often 
much  confused.  In  this  equatorial  belt,  the  cloudi- 
ness is  high  throughout  the  year,  averaging  .7  to  .8, 
with  a  relatively  small  annual  period.  The  data  and 
curve  following  are  fairly  typical,  but  the  annual 
period  varies  greatly  under  local  controls.  (Fig.  21). 


94 


CLIMATE 


TABLE  SHOWING   MONTHLY   DISTRIBUTION   OF   RAINFALL   FOR 
SELECTED    TROPICAL    STATIONS  1 


Tropics 

Double  Rainy 

Single  Rainy  Season 

• 

Season 
Equatorial 

Margin  of  Tropics 

Trade 
Rains 

Monsoon 
Rains 

Southern 

Northern 

Southern 
Africa 

Quito 

Sao 
Paulo 

Mexico 

Hilo 

Port 
Darwin 

Latitude 

6°S. 

Equator 

23.  5°  S. 

19.4°  N. 

19.7°  N. 

12.5°  S. 

Jan. 

86 

77 

195 

7 

79 

241 

Feb. 

80 

92 

156 

9 

94 

215 

March 

123 

115 

103 

26 

86 

166 

April 

195 

165 

58 

26 

94 

61 

May 

91 

109 

60 

85 

66 

23 

June 

10 

35 

46 

174 

55 

1 

July 

7 

25 

19 

180 

82 

0 

Aug. 

17 

52 

31 

207 

81 

2 

Sept. 

37 

60 

60 

179 

73 

5 

Oct. 

61 

91 

82 

79 

88 

38 

Nov. 

188 

94 

74 

20 

95 

72 

Dec. 

105 

85 

116 

8 

107 

176 

TABLE   SHOWING    MONTHLY  DISTRIBUTION   OF   CLOUDINESS   IN   AN 
EQUATORIAL    CLIMATE.       (CAMEROONS;    GABOON.       LAT.    3° 

N.,   WEST  AFRICA.) 

Jan.  Feb.  Mar.  Apr.  May  June  July  Aug.  Sept.  Oct.  Nov  Dec.  Year 
5.4      6.3     7.0      7.2     7.4     7.7     8.9     8.6      8.4      8.0      7.4     6.6      7.4 

At  greater  distances  from  the  equator  than  about 
10°  or  12°,  the  sun  is  still  vertical  twice  a  year  within 
the  tropics,  but  the  interval  between  these  two  dates 
is  so  short  that  the  two  rainy  seasons  merge  into  one, 
in  summer,  and  there  is  also  but  one  dry  season,  in 

1  The  figures  in  this  table  are  thousandths  of  the  mean  annual 
rainfall.  In  the  first  column  of  the  table,  the  average  of  a  con- 
siderable number  of  stations  is  given. 


CHARACTERISTICS   OF   ZONES— TROPICS       95 

winter.  This  is  the  so-called  tropical  type  of  rain- 
fall,1 and  is  found  where  the  trade  belts  are  encroached 
upon  by  the  equatorial  rains  during  the  migration  of 
these  rains  into  each  hemisphere.  It  is  illustrated  in 


J.    F.    M.    A.    M.    J.    J.    A.    S.    0.    N.    D.    J. 


M 


M 


FIG.  21.    ANNUAL  MARCH  OF  CLOUDINESS  IN  THE  TROPICS 
E:  Equatorial  type.     M:  Monsoon  type 


the  data  and  curves  for  Sao  Paulo,  Brazil,  and  for  the 
city  of  Mexico  (see  rainfall  table  above  and  Fig.  20) . 
The  mean  annual  rainfall  at  Sao  Paulo  is  54.13 
inches,  and  at  Mexico  22.99  inches. 

The  districts  of  tropical  rains  of  this  type  lie  along 
the  equatorial  margins  of  the  torrid  zone,  outside  of 
the  latitudes  of  the  equatorial  type  of  rainfall.  The 
rainy  season  becomes  shorter  with  increasing  distance 
from  the  equator.  The  weather  of  the  opposite  sea- 
sons is  strongly  contrasted.  The  single  dry  season 
lasts  longer  than  either  dry  season  in  the  equatorial 


1  Supan  calls  it  the  marginal  type  of  the  tropics. 


96  CLIMATE 

belt,  reaching  eight  months  in  typical  cases,  with  the 
wet  season  lasting  four  months.  The  lowlands  often 
become  dry  and  parched  during  the  long,  dry  trade 
wind  season  (winter),  and  vegetation  withers  away, 
while  grass  and  flowers  grow  in  great  abundance 
and  all  life  takes  on  new  activity  during  the  time 
when  the  equatorial  rainy  belt,  with  its  calms,  variable 
winds,  and  heavy  rains,  is  over  them  (summer) .  The 
Sudan  lies  between  the  Sahara  and  the  equatorial 
forests  of  Africa.  It  receives  rains,  and  its  vegeta- 
tion grows  actively,  when  the  doldrum  belt  is  north 
of  the  equator  (May- August).  But  when  the  trades 
blow  (December-March),  the  ground  is  parched  and 
dusty.  The  Venezuelan  llanos  have  a  dry  season  in 
the  northern  winter,  when  the  trade  blows.  The 
rains  come  in  May-October.  The  campos  of  Brazil, 
south  of  the  equator,  have  their  rains  in  October- 
April,  and  are  dry  the  remainder  of  the  year.  The 
Nile  overflow  results  from  the  rainfall  on  the  mount- 
ains of  Abyssinia  during  the  northward  migration 
of  the  belt  of  equatorial  rains. 

Simple  tropical  rainfalls,  as  showrn  in  the  above 
curves,  are  typical  of  large  areas,  but  they  are  not  in- 
frequently complicated  by  association  with  trade  or 
monsoon  rains,  as  in  the  West  Indies,  Central  Amer- 
ica, and  India.  The  true  doldrum  rains  may  come 
along  the  polar  margin  of  the  equatorial  low-pressure 
belt,  when  this  belt  is  moving  equatorward,  followed 
by  the  trades. 
The  so-called  tropical  type  of  temperature  variation, 


J.  F.  M.A.M.  J.  J.  A.  S.  0.  N..D. 


J.  F.  M.A.  M.  J.  J.  A.  S.  0.  N.  D.  J. 


5QO 


FIG.  22.    ANNUAL  MARCH  OF  TEMPERA- 
TURE:    TROPICAL  TYPE 

W:  Wadi  Haifa.     N:  Nagpur.     A:  Alice 

Springs.      H:    Honolulu.     J:  Jamestown, 

St.  Helena 


97 


98  CLIMATE 

with  one  maximum  and  one  minimum,  is  illustrated 
in  the  data  given  in  the  table  on  page  90,  and 
in  the  accompanying  curves  for  Wadi  Haifa,  in  Up- 
per Egypt;  Alice  Springs,  Australia;  Nagpur,  India; 
Honolulu,  Hawaii,  and  Jamestown,  St.  Helena. 
The  effect  of  the  rainy  season  is  often  shown  in  a 
displacement  of  the  time  of  maximum  temperature  to 
an  earlier  month  than  the  usual  one.  During  the 
rains,  the  temperature  is  apt  to  remain  constant,  as 
in  the  case  of  Nagpur,  and  of  other  stations  in 
India,  Mexico,  and  the  interior  of  Senegambia.  This 
type  of  temperature  curve  is  characteristic  of  most 
of  the  tropics  outside  of  the  latitudes  reached  by  the 
equatorial  belt. 

II.  Trade  Wind  Belts.  The  trade  belts  near 
sea-level  are  characterised  by  fair  weather,  steady 
winds,  infrequent  light  rains  or  even  an  almost  com- 
plete absence  of  rain ;  very  regular,  although  slight, 
annual  and  diurnal  ranges  of  temperature,  and  a 
constancy  and  regularity  of  weather  which  is  more 
truly  "  temperate  "  than  that  of  most  of  the  so-called 
temperate  zone.  The  climate  of  the  ocean  areas  in 
the  trade  wind  belts  is  indeed  the  simplest  and  most 
equable  in  the  world,  the  greatest  extremes — and  even 
these  are  moderate — being  found  to  leeward  of  the 
larger  lands,  where  the  continental  conditions  are 
carried  offshore  by  the  prevailing  winds.  On  the 
lowlands  swept  over  by  the  trades,  beyond  the  polar 
limits  of  the  equatorial  rain  belt  (roughly  between 
lats.  20°  and  30°) ,  are  most  of  the  great  deserts  of  the 


CHARACTERISTICS  OF  ZONES— TROPICS       99 

i 

world.  These  deserts  extend  directly  to  the  water's 
edge  on  the  leeward,  western  coasts  of  Australia, 
south  Africa,  and  South  America.  In  the  two  lat- 
ter regions,  the  desert  conditions  are  further  helped 
by  the  presence  of  cold  ocean  currents  offshore.  Be- 
cause of  their  great  extent,  these  trade  wind  deserts 
constitute  one  of  the  most  important  climatic  districts 
in  the  world. 

The  ranges  and  extremes  of  temperature  are  much 
greater  over  the  deserts,  especially  the  continental  in- 
teriors, than  over  the  oceans  of  the  trade  wind  belts. 
Minima  of  32°  or  less  occur  during  clear,  quiet  nights, 
and  daily  ranges  of  over  50°  are  common.  The  mid- 
summer mean  temperature  rises  above  90°,  with  noon 
maxima  of  110°,  or  more,  in  the  non-cloudy,  dry  air 
of  a  desert  day.  The  days,  with  high,  dry  winds, 
carrying  dust  and  sand,  with  extreme  heat,  accent- 
uated by  the  absence  of  vegetation,  are  disagreeable 
or  even  dangerous  to  life ;  but  the  calmer  nights,  with 
active  radiation  under  clear  skies,  are  much  more 
comfortable.  The  nocturnal  temperatures  are  even 
not  seldom  too  low  for  comfort  in  the  cooler  season, 
when  thin  sheets  of  ice  may  form.  Under  the  strong 
insolation  by  day  and  the  quick  cooling  by  night, 
rocks  iriLthe  deserts  split  and  break  up.  On  the  whole, 
however,  man  is  less  susceptible  to  the  larger  tem- 
perature ranges  in  tropical  deserts  than  to  the  smaller 
ones  in  the  equatorial  belt,  because  of  the  lower  rela- 
tive humidity  in  the  former  case.  •  In  the  trade  wind 
deserts,  as  in  other  arid  regions,  man  is  nomadic. 


100  CLIMATE 

While  the  trades  are  drying  winds  as  long  as  they 
blow  strong  over  the  oceans,  or  over  lowlands,  they 
contain  a  large  amount  of  water  vapour,  and  readily 
become  rainy  if  they  are  cooled  during  an  ascent 
over  a  mountain  or  highland.  Hence  the  windward 
(eastern)  sides  of  mountains  or  bold  coasts  in  the 
trade  wind  belts  are  well  watered,  while  the  leeward 
sides,  or  interiors,  are  dry.  Mountainous  islands  in 
the  trades,  like  the  Hawaiian  Islands,  many  of  the 
East  and  West  Indies,  the  Philippines,  Borneo,  Cey- 
lon, Madagascar,  Teneriffe,  etc.,  show  marked  diver- 
gences of  this  sort.  The  eastern  coasts  of  Guiana, 
Central  America,  south-eastern  Brazil,  south-eastern 
Africa,  and  eastern  Australia  are  well  watered,  while 
the  interiors  are  very  dry  in  the  two  last-named  coun- 
tries. The  eastern  highland  of  Australia  constitutes 
a  more  effective  barrier  than  that  in  south  Africa; 
hence  the  Australian  interior  has  a  more  extended 
desert.  South  America  in  the  south-east  trade  belt  is 
not  well  enclosed  on  the  east,  and  the  most  arid  por- 
tion is  an  interior  district  near  the  eastern  base  of 
the  Andes,  where  the  land  is  IOWT.  Even  far  inland, 
the  Andes  again  provoke  precipitation  along  their 
eastern  base,  and  the  narrow  Pacific  coastal  strip,  to 
leeward  of  the  Andes,  is  a  very  pronounced  desert 
from  the  equator  to  about  lat.  30°  S.  The  cold  ocean 
waters,  with  prevailing  southerly  (drying)  winds 
alongshore,  are  additional  factors  in  causing  this 
aridity.  The  Peruvian  climatic  province  is  abnorm- 
ally cool.  Highlands  in  the  trade  belts  are  therefore 


CHARACTERISTICS  OF  ZONES-- TROPICS     101 

moist  on  their  windward  slopes — even  in  deserts, 
mountains  provoke  local  rainfall,  tree  growth,  and 
local  streams — and  becomes  oases  of  luxuriant  plant 
growth,  while  close  at  hand,  on  the  leeward  sides,  dry 
savannas  or  deserts  may  be  found. '  The  damp,  rainy 
and  forested  windward  (N.E.  trade)  side  of  Central 
America  was,  from  the  earliest  days  of  European  oc- 
cupation, left  to  the  natives,  while  the  centre  of  civili- 
sation was  naturally  established  on  the  more  open  and 
sunny  south-western  side. 

The  rainfall  associated  with  the  conditions  just  de- 
scribed is  known  as  the  trade  type.  These  rains  have 
a  maximum  in  winter,  when  the  trades  are  most  ac- 
tive, this  being  a  departure  from  the  general  rule  of 
summer  rains  in  the  tropics.  In  cases  where  the  trade 
blows  steadily  throughout  the  year  against  mount- 
ains or  bold  coasts,  as  on  the  Atlantic  coast  of  Cen- 
tral America,  there  is  no  really  dry  season. )  The  data 
and  curve  for  Hilo  (mean  annual  rainfall  145.24 
inches),  on  the  windward  side  of  the  Hawaiian 
Islands,  show  typical  conditions  (see  Fig.  20).  The 
tropical  rains  are  convectional,  and  therefore  prefer 
the  warm  season;  the  trade  rains  are  orographic,  and 
have  a  winter  maximum. 

Many  combinations  of  different  rainfall  types  are 
found  in  the  trade  wind  latitudes.  Zanzibar,  for 
example  (lat.  6°  12'  S.,  long.  39°  19'  E.),  has  two  equa- 
torial rainfall  maxima  (April-May;  November),  which 
come  soon  after  the  vertical  sun,  but  are  associated 
with  monsoon  winds.  Again,  on  the  lee  of  high- 


102  CLIMATE 

lands  which  receive  a  winter  maximum  on  their 
windward  slopes,  summer  rains  may  occur  at  the 
time  when  the  trade  is  weakest,  and  the  otherwise 
long  dry  season  is  interrupted  by  scattering  showers. 
In  the  Malay  archipelago,  there  are  complications 
of  equatorial  and  trade  rains;  likewise  in  the  West 
Indies.  Trade  rains  often  have  a  tendency  to  give 
precipitation  both  day  and  night,  while  torrid  zone 
rains  generally  prefer  the  day.  ^ 

III.  Monsoon  Belts.  In  a  typical  monsoon  re- 
gion, such  as  that  of  India,  eastern  Asia,  and  the  ad- 
jacent islands,  the  rains  follow  the  vertical  sun,  and 
therefore  have  a  simple  annual  period  much  like  that 
of  the  tropical  type  above  described,  the  dry  season 
coming  when  the  sun  is  lowest  (winter) .  This  mon- 
soon type  of  rainfall  is  well  illustrated  in  the  data 
and  curve  for  Port  Darwin  (mean  annual  rainfall 
62.72  inches),  in  Australia.  This  summer  monsoon 
rainfall  results  from  the  inflow  of  a  large  body  of 
warm,  moist  air  from  the  sea  on  to  a  land  area ;  a  con- 
sequent retardation  of  the  velocity  of  the  air  currents, 
as  the  result  of  friction,  and  an  ascent  of  the  air,  the 
rainfall  being  particularly  heavy  where  the  winds 
have  to  climb  over  high  lands.  Thus,  in  India,  the 
precipitation  is  heaviest  at  the  head  of  the  Bay  of 
Bengal,  where  Cherrapunji,  at  the  height  of  4455 
feet  in  the  Khasi  Hills,  has  a  mean  annual  rainfall  of 
between  400  and  500  inches;  along  the  southern  base 
of  the  Himalayas  (60  to  160  inches)  ;  on  the  bold 
western  coast  of  the  peninsula  (80  to  120  inches  and 


CHARACTERISTICS  OF  ZONES— TROPICS     103 

over),  and  on  the  mountains  of  Burma  (up  to  160 
inches).  In  the  rain-shadow  of  the  Western  Ghats, 
the  Deccan  often  suffers  from  drought  and  famine 
unless  the  monsoon  rains  are  abundant  and  well  dis- 
tributed, and  the  decreasing  rainfall  up  the  Ganges 
valley  leaves  the  Indus  plain  with  a  deficiency  (less 
than  five  inches).  The  prevailing  direction  of  the 
rainy  monsoon  wind  in  India  is  south-west;  on  the 
Pacific  coast  of  Asia,  south-east.  This  monsoon  dis- 
trict is  very  large,  including  the  Indian  Ocean,  Ara- 
bian Sea,  Bay  of  Bengal,  and  adjoining  continental 
areas;  the  Pacific  coast  of  China,  the  Yellow  and 
Japan  seas,  and  numerous  islands  from  Borneo  to 
Sakhalin  on  the  north  and  to  the  Ladrone  Islands  on 
the  east.  Where  the  seasons  are  clearly  defined  in 
India,  they  are  three  in  number:  a  cool,  dry  season 
(winter)  when  northerly  trade  winds  prevail,  and 
when  there  is  little  or  no  rainfall  except  in  the  north- 
ern provinces,  where  moderate  cyclonic  storms  oc- 
casionally occur ;  a  wet  season,  sultry  and  oppressive, 
with  the  inflowing  south-west  monsoon  of  summer; 
and  a  hot,  dry  season  before  the  beginning  of  the 
rains.  The  beginning  of  the  monsoon  rains  usually 
comes  suddenly  ("burst"),  with  heavy  thunder- 
storms. A  typical  temperature  curve  for  a  monsoon 
district  is  that  for  Nagpur,  in  the  Indian  Deccan 
(see  Fig.  22),  and  a  typical  cloudiness  curve  is  given 
in  Fig.  21,  the  maximum  coming  near  the  time  of  the 
vertical  sun,  in  the  rainy  season,  and  the  minimum  in 
the  dry  season. 


104  CLIMATE 

TABLE    SHOWING    MONTHLY    DISTRIBUTION    OF    CLOUDINESS    IN    A 

MONSOON   CLIMATE    (BENGAL,   LAT.   23.5°    N.).1 

Jan.  Feb.  Mar.  Apr.  May  June  July  Aug.  Sept.  Oct.  Nov.  Dec.  Year 

1.9     1.8     2.6    3.0    4.5     7.5      8.5      8.4      7.5    4.3     2.5      1.8    4.5 

In  the  Australian  monsoon  region,  which  reaches 
across  New  Guinea  and  the  Sunda  Islands,  and  west 
of  Australia,  in  the  Indian  Ocean,  over  latitudes 
0°-10°  S.,  the  monsoon  rains  come  with  north-west 
winds  in  the  period  between  November  and  March  or 
April.  The  northern  portion  of  Australia  is  thus 
watered  by  zenithal  summer  rains,  and  the  southern 
portions  of  Sumatra,  Borneo,  and  Java  are  also  un- 
der the  influence  of  this  north-west  monsoon.  The 
essential  features  of  the  whole  Indo- Australian  mon- 
soon belt,  therefore,  are  a  fairly  uniform  distribution 
and  small  annual  range  of  temperature;  and  well- 
marked  periodic  rains,  coming  with  north-west  or 
south-west  winds  according  to  the  hemisphere. 

The  general  rule  that  eastern  coasts  in  the  tropics 
are  the  rainiest  finds  exceptions  in  the  case  of  the  rainy 
western  coasts  in  India  and  other  districts  with  simi- 
lar rains.  On  the  coast  of  the  Gulf  of  Guinea,  for 
example,  there  is  a  small  rainy  monsoon  area  during 
the  summer;  heavy  rains  fall  on  the  seaward  slopes  of 
the  Cameroon  Mts.  Not  far  inland,  Baliburg  shows 
a  double  maximum  of  the  equatorial  type.  Goree, 
lat.  15°  N.,  on  the  coast  of  Senegambia,  gives  a  fine 
example  of  a  rainy  (summer)  and  a  dry  (winter) 
monsoon.  A  case  of  a  special  kind  is  the  Somali 

1  Five  stations. 


CHARACTERISTICS   OF  ZONES— TROPICS     105 

coast,  which  trends  N.E-S.W.,  and  is  therefore 
parallel  with  both  monsoons.  Hence  at  no  season 
can  it  become  very  rainy,  and  mean  annual  rainfalls 
of  40  inches  are  not  recorded  until  the  coast  takes  a 
turn  to  the  south,  at  Mombasa. 

Numerous  combinations  of  equatorial,  trade  and 
monsoon  rainfalls  are  found,  often  creating  great 
complexity.  In  the  case  of  Port  Darwin,  the  station 
is  near  enough  to  the  equator  to  have  two  rainy  sea- 
sons (equatorial  type)  when  the  sun  is  vertical,  as  is 
frequently  the  case  in  the  West  Indies  and  Central 
America  in  the  same  latitude.  The  rainiest  month, 
however,  is  January,  between  the  two  times  of  verti- 
cal sun,  but  during  the  height  of  the  monsoon,  there 
being  a  rainy  season  of  four  months  and  a  dry  season 
of  eight  months.  The  monsoon  thus  interferes  with 
the  typical  occurrence  of  equatorial  rains.  It  is  also 
true  that  the  dry  season  in  monsoon  districts  is  drier 
than  the  two  dry  seasons  of  the  equatorial  type. 
Batavia,  on  the  island  of  Java,  has  simple  monsoon 
rains.  Buitenzorg,  on  the  same  island,  has  a  mon- 
soon maximum  in  January,  two  months  before  the 
sun  is  vertical  for  the  first  time,  and  it  has  a  regular 
tropical  maximum  of  rainfall  in  October,  following 
the  second  zenithal  position  of  the  sun.  The  north 
coast  of  Ceram,  in  the  Moluccas,  has  north-west  sum- 
mer monsoon  rains,  with  a  maximum  in  February, 
while  the  south  coast  has  winter  rains,  with  the  south- 
east trade.  The  rainy  and  dry  seasons  thus  corne 
under  different  conditions  and  at  opposite  times  on 


106  CLIMATE 

the  two  coasts.  These  two  sets  of  conditions  are 
often  very  close  together,  with  a  divide  between  them. 
On  the  island  of  Hawaii,  Hilo,  on  the  east  side,  is 
exposed  to  the  north-east  trade  and  has  a  winter  maxi- 
mum of  rainfall.  Kailua,  on  the  lee  side,  has  about 
one-third  as  much  rainfall,  with  a  summer  maximum. 
The  islands  of  the  East  Indian  archipelago  furnish 
many  examples  of  such  curious  complications.  The 
eastern  coast  of  Madagascar  has  south-east  trade 
winds  fairly  uniformly  through  the  year,  while  the 
interior  and  west  coast  have  a  summer  maximum— 
the  normal  tropical  rainfall  season. 

IV.  Mountain  Climate.  Within  the  tropics,  alti- 
tude is  chiefly  important  because  of  its  effect  in  tem- 
pering the  heat  of  the  lowlands,  especially  at  night. 
If  tropical  mountains  are  high  enough,  they  carry 
snow  the  year  around,  even  on  the  equator,  and  the 
zones  of  vegetation  may  range  from  the  densest 
tropical  forest  at  their  base  to  the  snow  on  their  sum- 
mits. The  highlands  and  mountains  within  the 
tropics  are  thus  often  sharply  contrasted  with  the 
lowlands,  and  offer  more  agreeable  and  more  healthful 
conditions  for  white  settlement.  They  are  therefore 
often  sought  out  by  residents  from  colder  latitudes 
as  the  most  attractive  resorts.  In  India,  the  hill  sta- 
tions are  crowded  during  the  hot  months  by  civilian 
and  military  officials,  and  it  has  been  well  said  that 
India  is  ruled  from  7,000  feet  above  sea-level.  The 
climate  of  many  tropical  plateaus  and  mountains 
has  the  reputation  of  being  a  "  perpetual  spring." 


CHARACTERISTICS   OF  ZONES— TROPICS     107 

Thus,  on  the  interior  plateau  of  the  tropical  Cordil- 
leras of  South  America,  and  on  the  central  plateau  of 
tropical  Africa,  the  heat  is  tempered  by  the  altitude, 
while  the  lowlands  and  coasts  '  are  very  hot.  The 
rainfall  on  tropical  mountains  and  highlands  often 
differs  considerably  in  amount  from  that  on  the 
lowlands,  and  other  features  common  to  mountain 
climates  the  world  over  are  also  noted.  But  the 
main  emphasis  is  rightly  laid  upon  the  temperature. 


CHAPTER  V 

THE  CHARACTERISTICS  OF  THE  ZONES:  II.— THE 
TEMPERATE  ZONES 

General :  "  Temperate  "  Zones — Temperature — Pressure  and  Winds 
— Rainfall — Humidity  and  Cloudiness — Seasons:  Their  Effects 
on  Man — Weather — Climatic  Subdivisions — South  Temperate 
Zone — Sub-tropical  Belts:  Mediterranean  Climates — North 
Temperate  Zone:  Western  Coasts — Interiors — Eastern  Coasts 
— Mountain  Climates. 

General:  "Temperate"  Zones.  The  so-called 
"  temperate "  zones  occupy  about  one-half  of  the 
earth's  surface.  As  a  whole,  they  are  temperate  only 
in  that  their  mean  temperatures  and  their  physiolo- 
gical effects  are  intermediate  between  those  of  the 
tropics  and  those  of  the  polar  zones.  The  modifica- 
tions of  solar  climate  which  result  from  the  distribu- 
tion and  influence  of  land  and  water  are  greatest  in 
the  temperate  zones.  The  north  temperate  zone  in- 
cludes the  greatest  known  extremes  of  temperature. 
If  the  use  of  the  word  "  temperate "  were  not  so 
firmly  established  it  would  be  well  to  change  the  name 
to  intermediate,  or  to  middle.1 

1  North-middle  and  south-middle  would  then  distinguish  the 
zones  in  the  two  hemispheres.  (See  W.  M.  Davis:  The  Temperate 
Zones,  Journ.  Geogr.,  vol.  i,  1897,  pp.  139-143.)  "  Temperate  "  does, 
however,  apply  fairly  well  to  the  south  temperate  zone. 

108 


CHARACTERISTICS  OF  ZONES— TEMPERATE  109 

A  marked  changeableness  of  the  weather  is  a  strik- 
ing characteristic  of  these  zones.  Apparently  irreg- 
ular and  haphazard,  these  continual  weather  changes 
nevertheless  run  through  a  fairly  systematic  series, 
although  they  are  essentially  non-periodic.  Climate 
and  weather  are  by  no  means  synonymous  over  most 
of  the  extra-tropical  latitudes. 

Temperature.  The  mean  annual  temperatures  at 
the  margins  of  the  north  temperate  zone  differ  by 
more  than  70°.  The  ranges  between  the  mean  tem- 
peratures of  hottest  and  coldest  months  reach  120°  at 
their  maximum  in  north-eastern  Siberia,  and  80°  in 
North  America.  A  January  mean  of  —60°  and  a 
July  mean  of  95°,  and  maxima  of  over  120°  and 
minima  of  — 90°,  occur  in  the  same  zone.  In  the  dis- 
tricts of  lowest  winter  minima,  the  mean  summer  tem- 
peratures exceed  85°,  and  in  portions  of  the  districts 
of  highest  mean  summer  maxima,  the  mean  winter 
minima  fall  below  32°.  Such  great  ranges  character- 
ise the  extreme  land  climates.  Under  the  mild  in- 
fluence of  the  oceans,  the  windward  west  coasts  have 
much  smaller  ranges  than  the  interiors;  the  seasonal 
differences  increase  inland.  The  annual  ranges  in 
the  middle  and  higher  latitudes  exceed  the  diurnal, 
the  conditions  in  much  of  the  torrid  zone  being  ex- 
actly reversed.  Over  much  of  the  oceans  of  the  tem- 
perate zones  the  annual  range  is  less  than  10°.  In 
the  south  temperate  zone  there  are  no  extreme  ranges, 
the  maxima,  slightly  over  30°,  being  near  the  margin 
of  the  zone  in  the  interior  of  South  America,  south 


110  CLIMATE 

Africa,  and  Australia.  In  these  same  localities,  the 
diurnal  ranges,  however,  rival  those  of  the  north 
temperate  zone. 

The  north-eastern  Atlantic  ocean  and  north-west- 
ern Europe  are  about  35°  too  warm  for  their  latitude 
in  January,  while  north-eastern  Siberia  is  30°  too  cold. 
The  lands  north  of  Hudson's  Bay  are  25°  too  cold, 
and  the  waters  of  the  Alaskan  Bay  20°  too  warm. 
In  July,  and  in  the  southern  hemisphere,  the  anoma- 
lies are  small.  The  lands  which  are  the  centre  of 
civilisation  in  Europe  average  too  warm  for  their  lati- 
tudes. These  lands  are  the  most  truly  "  temperate  " 
portion  of  the  north  temperate  zone.  The  north- 
west coast  of  North  America  is  much  the  same.  The 
diurnal  variability  of  temperature  is  greater  in  the 
north  temperate  zone  than  elsewhere  in  the  world, 
and  the  same  month  may  differ  greatly  in  its  charac- 
ter in  different  years.  One  winter  in  higher  latitudes 
may  have  much  snow,  and  temperatures  below 
normal ;  the  next  may  give  much  rain  instead  of  snow, 
and  the  ground  remain  unfrozen.  One  summer  may 
be  very  favourable  for  crops;  the  next  may  give  a 
poor  harvest. 

From  the  point  of  view  of  temperature,  these  zones 
may  be  considered  in  three  divisions:  (1)  the  sub- 
tropical, (2)  the  "temperate"  latitudes,  and  (3)  the 
sub-polar.  The  annual  temperature  curve  has  one 
maximum  and  one  minimum.  In  the  continental 
type,  the  times  of  maximum  and  minimum  are  about 
one  month  behind  the  maximum  and  minimum  in- 


CHARACTERISTICS  OF  ZONES— TEMPERATE  111 

solation  dates.  In  the  marine  type,  the  retardation 
may  amount  to  nearly  two  months.  Coasts  and 
islands  have  a  tendency  to  a  cool  spring  and  warm 
autumn;  continents,  to  similar  temperatures  in  both 
spring  and  fall. 

Pressure  and  Winds.  The  prevailing  winds  are 
the  "  westerlies,"  which  occupy  about  as  much  of  the 
earth's  surface  as  do  the  easterly  trades.  The  wester- 
lies are,  however,  much  less  regular  than  the  trades. 
They  vary  greatly  in  velocity  in  different  regions  and 
in  different  seasons,  from  a  light  wind  to  a  gale  of 
fifty  or  more  miles  an  hour.  They  are  stronger  in 
winter  than  in  summer.  They  are  much  interfered 
with,  especially  in  the  higher  northern  latitudes,  by 
seasonal  changes  of  temperature  and  pressure  over  the 
continents,  whereby  the  latter  establish,  more  or  less 
successfully,  a  system  of  obliquely  outflowing  winds 
in  winter  and  of  obliquely  inflowing  winds  in  sum- 
mer. On  the  eastern  coast  of  Asia  there  is  a  com- 
plete reversal  in  wind  direction  at  the  opposite 
seasons,  but  usually  the  seasonal  shift  is  much  less 
than  180°.  In  summer,  when  the  lands  have  low 
pressure,  the  northern  oceans  are  dominated  by  great 
oval  areas  of  high  pressure,  with  outflowing  spiral 
eddies,  while  in  winter,  wiien  the  northern  lands  have 
high  pressure,  the  northern  portions  of  the  oceans 
develop  cyclonic  systems  of  inflowing  winds  over 
their  warm  waters.  All  these  great  continental  and 
oceanic  systems  of  spiraling  winds  are  important 
climatic  controls. 


112  CLIMATE 

The  westerlies  are  also  much  confused  and  inter- 
rupted by  storms.  Hence  their  designation  of  stormy 
westerlies.  A  constant  succession  of  cyclones,  and 
the  accompanying  anticyclones,  travelling  along  with 
the  prevailing  westerlies,  causes  the  latter  very  fre- 
quently to  change  direction  in  order  to  become  part 
of  a  cyclonic  or  an  anticyclonic  whirl.  In  these 
storms,  velocities  of  eighty  or  more  miles  an  hour 
may  be  reached  at  sea.  So  common  are  such  in- 
terruptions that  the  prevailing  westerly  wind  direc- 
tion is  often  difficult  to  discern  without  careful 
observation.  Cyclonic  storms  are  most  numerous 
and  best  developed  in  winter.  The  irregular  press- 
ure changes  usually  wholly  mask  the  faint  diurnal 
variation  of  the  barometer  which  is  so  characteristic 
of  the  tropics,  and  which  becomes  less  and  less  marked 
with  increasing  latitude.  Although  greatly  inter- 
fered with  near  sea-level  by  continental  changes  of 
pressure,  by  cyclonic  and  anticyclonic  whirls,  and  by 
local  inequalities  of  the  surface,  the  eastward  move- 
ment of  the  atmosphere  remains  very  constant  aloft. 
The  drift  of  the  higher  clouds,  and  wind  observations 
on  mountains,  show  clearly  that  the  upper  currents 
blow  with  great  steadiness  from  westerly  points,  the 
departures  being  temporary,  and  under  the  control 
of  passing  cyclones  or  anticyclones.  The  south  tem- 
perate zone  is  chiefly  water.  Hence  the  westerlies 
are  but  little  distorted  by  continental  effects.  They 
are  strong  and  steady,  and  almost  as  regular  as  the 
trades.  "  Roaring  forties  "  is  a  well-known  designa- 


CHARACTERISTICS  OF  ZONES— TEMPERATE  113 

tion  for  the  southern  middle  latitudes,  and  between 
latitudes  40°  and  60°  S.  the  "  brave  west  winds  "  blow 
with  a  constancy  and  a  velocity  found  in  the  northern 
hemisphere  only  on  the  oceans,  and  then  in  a  modi- 
fied form.  Storms,  frequent  and  severe,  character- 
ise these  southern  hemisphere  westerlies,  and  easterly 
wind  directions  are  temporarily  noted  during  their 
passage.  Voyages  to  the  west  around  Cape  Horn 
against  head  gales,  and  in  cold,  wet  weather,  are 
much  dreaded.  South  of  Africa  and  Australia,  also, 
the  westerlies  are  remarkably  steady  and  strong. 
The  winter  in  these  latitudes  is  stormier  than  the 
summer,  but  the  seasonal  difference  is  less  than  that 
north  of  the  equator. 

Between  trades  and  westerlies  lies  a  debatable  belt 
of  high  pressure,  shifting  seasonally.  Within  it, 
stormy  westerlies  and  drying  trades  alternately  hold 
sway.  It  is  the  sub-tropical  belt,  a  favoured  climatic 
region,  where  invalids  seek  health,  and  an  escape  from 
the  rigors  of  a  cold  winter  is  found  by  many  who 
have  time  and  means  to  leave  their  northern  homes. 

Rainfall.  Rainfall  is  fairly  abundant  over  the 
oceans,  where  evaporation  is  large,  and  also  over  a 
considerable  part  of  the  lands  (30-80  inches,  and 
more) .  It  comes  chiefly  in  connection  with  the  usual 
cyclonic  storms,  or  in  thunderstorms,  but  altitude 
often  serves  locally  to  increase  this  precipitation.  So 
great  are  the  differences,  geographic  and  periodic,  in 
rainfall,  produced  by  differences  in  temperature, 
topography,  cyclonic  conditions,  etc.,  that  none  but 


114  CLIMATE 

the  most  general  rules  can  be  laid  down.  The 
equatorward  margin  of  the  temperate  zone  rains  is 
clearly  defined  on  the  west  coasts,  at  the  points  where 
the  coast  deserts  are  replaced  by  belts  of  light  or 
moderate  rainfall.  Bold  west  coasts,  on  the  polar 
side  of  lat.  40°,  are  very  rainy,  having  100  inches  and 
more  a  year  in  the  most  favourable  situations.  The 
hearts  of  the  continents,  far  from  the  sea,  and  especi- 
ally when  well  enclosed  by  mountains,  or  when  blown 
over  by  cool  ocean  winds  which  warm  in  crossing  the 
land,  have  light  rainfall  (less  than  10-20  inches). 
East  coasts,  receiving  rain  from  moist  winds  blowing 
in  from  the  adjacent  oceans  as  monsoons,  or  in  front 
of  cyclonic  storms,  are  wetter  than  interiors,  but  drier 
than  west  coasts.  Winter  is  the  season  of  maximum 
rainfall  over  oceans,  islands,  and  west  coasts,  for  the 
westerlies  are  then  most  active,  cyclonic  storms  are 
then  most  numerous  and  best  developed,  and  the  cold 
lands  chill  the  inflowing  damp  air.  At  this  season, 
however,  the  low  temperatures,  high  pressures,  and 
tendency  to  outflowing  winds  over  the  continents  are 
unfavourable  to  rainfall,  and  the  interior  land  areas, 
as  a  rule,  then  have  their  minimum.  The  warmer 
months  bring  the  maximum  rainfall  over  the  conti- 
nents. Then  conditions  are  favourable  for  inflowing 
damp  winds  from  the  adjacent  oceans;  there  is  the 
best  opportunity  for  convection;  thunder-showers 
readily  develop  on  the  hot  afternoons ;  the  capacity  of 
the  air  for  water  vapour  is  greatest.  Continents, 
from  equator  to  higher  latitudes,  thus  have  a  tend- 


CHARACTERISTICS  OF  ZONES— TEMPERATE  115 

ency  to  maximum  rainfall  in  the  warm  season;  sum- 
mer rains,  as  a  whole,  predominate  over  the  lands. 
The  marine  type  of  rainfall,  with  a  winter  maximum, 
extends  in  over  the  western  borders  of  the  continents, 
and  is  also  found  in  the  winter  rainfall  of  the  sub- 
tropical belts.  These  winter  rains  are  in  some  respects 
like  the  winter  rains  on  windward  coasts  in  the  trades. 
Coastal  lands  reached  by  them  are  well  watered,  and 
droughts  need  not  be  feared.  Rainfalls  are  heaviest 
along  the  tracks  of  most  frequent  cyclonic  storms. 

For  continental  stations,  the  typical  daily  march  of 
rainfall  is  shown  in  the  accompanying  data  for  Berlin 
and  New  York. 

DAILY  MARCH  OF  RAINFALL  (THOUSANDTHS  OF  THE  DAILY 

MEAN). 

I.     Continental  Type. 
Hours.  Berlin.         New  York. 

12  P.M.— 2     A.M 76  79 

2-4            83  85 

4-6            74  79 

6-8            69  80 

8-10          62  74 

10-Noon     68  81 

Noon — 2     P.M 85  83 

2-4            105  95 

4-6            104  91 

6-8            113  90 

^8-10          , 83  85 

10-12  P.M 78  78 

The  chief  maximum  is  in  the  afternoon,  and  the 
secondary  maximum  comes  in  the  night  or  early 
morning.  The  chief  minimum  comes  between  10  A.M. 
and  2  P.M.  Coast  stations  generally  have  a  night 


116  CLIMATE 

maximum,  and  a  minimum  between  10  A.M.  and  4 
P.M.,  as  illustrated  in  the  following  data  for  Valentia. 

DAILY     MARCH    OF    RAINFALL    AT    VALENTIA     (THOUSANDTHS    OF 

DAILY   MEAN) 
II.    Marine  Type. 

12p.M— 2  A.M 88 

2-4  93 

4-6  93 

6-8  90 

8-10  84 

10-Noon  76 

Noon — 2  P.M 74 

2-4  75 

4-6  80 

6-8  82 

8-10  82 

10-12  P.M 83 

Humidity  and  Cloudiness.  Arrhenius  gives  the 
mean  cloudiness  for  different  latitudes  as  follows: 

70°  N.  60°  50°  40°  30°  20°  10°  Eq.  10°  20°  30°  40°  50°  60°  S. 
59    61  48  49  42  40  50   58  57  48  46   5G   66  75 

The  higher  latitudes  of  the  temperate  zones  thus 
have  a  mean  cloudiness  which  equals  and  even  exceeds 
that  of  the  equatorial  belt.  The  amounts  over  the 
oceans  and  coasts  are  greater  than  inland.  The  belts 
of  minimum  cloudiness  are  at  about  lat.  30°  N.  and 
S.  Over  the  continental  interiors,  the  cloudiest  sea- 
son is  summer,  but  the  amount  is  never  very  large. 
Otherwise,  winter  is  generally  the  cloudiest  season, 
with  a  fairly  high  mean  annual  amount. 

The  absolute  humidity,  as  a  whole,  decreases  as  the 


CHARACTERISTICS  OF  ZONES— TEMPERATE  117 

temperature  falls.  The  relative  humidity  averages 
ninety  per  cent.,  more  or  less,  over  the  oceans,  and  is 
high  under  the  clouds  and  rain  of  cyclonic  storms,  but 
depends,  on  land,  upon  the  wind  direction;  winds 
from  an  ocean  or  from  a  lower  latitude  being  damper, 
and  those  from  a  continent  or  from  a  colder  latitude 
being  drier. 

Seasons:  Their  Effects  on  Man.  Seasons  in  the 
temperate  zones  are  classified  according  to  tempera- 
ture— not,  as  in  the  tropics,  by  rainfall.  The  four 
seasons  are  important  characteristics  of  these  zones, 
especially  of  the  middle  latitudes  of  the  north  tem- 
perate zone.  Here  spring  and  autumn  intervene  as 
transition  seasons  between  the  colder  winter  with 
snow,  and  warmer  summer  with  more  or  less  rain. 
Towards  the  equatorial  margins  of  the  zones,  the  dif- 
ference in  temperature  between  summer  and  winter 
becomes  smaller,  and  the  transition  seasons  weaken 
and  even  disappear.  At  the  polar  margins,  the 
change  from  winter  to  summer,  and  vice  versa,  is  so 
sudden  that  there  also  the  transition  seasons  dis- 
appear. These  seasonal  changes  are  of  the  greatest 
importance  in  the  life  of  man. 

Weather.  An  extreme  changeableness  of  the 
weather^  depending  on  the  succession  of  cyclones  and 
anticyclones,  is  another  characteristic.  For  most  of 
the  year  and  most  of  the  zone,  settled  weather  is  un- 
known. The  changes  are  most  rapid  in  the  northern 
portion  of  the  north  temperate  zone,  especially  on 
the  continents,  where  the  cyclones  travel  fastest.  The 


118  CLIMATE 

nature  of  these  changes  depends  on  the  degree  of  de- 
velopment, the  velocity  of  progression,  the  track,  and 
other  conditions  of  the  disturbance  which  produces 
them.  The  changes  may  be  sudden  and  marked,  or 
faint  and  slow;  the  wind  may  back  or  veer;  the  pre- 
cipitation may  be  heavy  or  light;  the  wind  velocity 
may  be  light,  or  of  hurricane  force;  anticyclones  may 
be  clear,  or  may  have  clouds,  and  not  infrequently, 
precipitation.  There  is  an  almost  endless  variety  of 
such  examples.  The  detailed  study  of  these  varying 
phases  of  cyclonic  and  anticyclonic  weather  controls 
belongs  to  meteorology.  It  suffices  here  to  say  that 
the  particular  weather  types  resulting  from  this  con- 
trol give  the  climates  their  distinctive  character,  and 
that  the  study  of  climate  through  these  types  is  the 
only  method  of  appreciating  the  actual  conditions. 
Annual  and  monthly  averages  of  the  different  cli- 
matic elements  alone  are  misleading,  and  give  but  a 
lifeless  picture.  The  cyclonic  unit,  although  its  period 
is  irregular  and  of  varying  length,  is  an  essential 
basis  of  computation  and  comparison. 

The  weather  types  vary  with  the  season  and  with 
the  geographical  position.  They  result  from  a  com- 
bination, more  or  less  irregular,  of  periodic,  diurnal 
elements,  under  the  regular  control  of  the  sun,  and 
of  non-periodic  cyclonic  and  anticyclonic  elements. 
In  summer,  on  land,  when  the  cyclonic  element  is 
weakest  and  the  solar  control  is  the  strongest,  the 
dominant  types  are  associated  with  the  regular 
changes  from  day  to  night.  Daytime  cumulus 


CHARACTERISTICS  OF  ZONES— TEMPERATE  119 

clouds;  diurnal  variation  in  wind  velocity;  afternoon 
thunderstorms,  with  considerable  regularity,  char- 
acterise the  warmest  months  over  the  continents  and 
present  an  analogy  with  tropical  conditions.  Cy- 
clonic and  anticyclonic  spells  of  hotter  or  cooler, 
rainy  or  dry,  weather,  with  varying  winds  differing 
in  the  temperatures  and  the  moisture  which  they 
bring,  serve  to  break  the  regularity  of  the  diurnal 
types.  On  the  oceans,  the  diurnal  characteristics  are 
much  less  marked. 

In  winter,  the  non-periodic,  cyclonic  control  is 
strongest.  Local  conditions  of  heat  and  cold  become 
subordinate  to  the  general  control  by  the  cyclone, 
which  imports  weather  from  a  distance.  The  irregu- 
lar changes  from  clear  to  cloudy,  from  warmer  to 
colder,  from  dry  air  to  snow  or  rain,  extend  over 
large  areas  and  show  little  diurnal  control.  Spring 
and  autumn  are  transition  seasons  and  have  transition 
weather  types.  In  spring,  the  growing  diurnal 
quality  is  marked  by  the  increasing  importance  of 
local  controls ;  the  appearance  of  convectional  pheno- 
mena such  as  spring  rains;  the  struggle  between  the 
cyclonic  and  the  solar  controls  of  temperature,  now 
one  and  now  the  other  being  paramount,  but  the  lat- 
ter gaining  and  the  former  losing.  Cold  spells,  with 
cyclonic  winds  and  clouds,  recall  winter.  Warm 
spells,  with  marked  diurnal  temperature  range,  pre- 
sage summer.  In  autumn,  the  decreasing  frequency 
and  importance  of  diurnal  phenomena,  such  as  thun- 
der-showers, high  afternoon  temperatures,  and  the 


120  CLIMATE 

like;  the  active  radiation  and  cooling  during  the 
longer  nights,  with  resulting  fogs;  and  the  increas- 
ing control  by  the  cyclone,  point  to  winter's  coming. 

Weather  types  thus  differ  with  the  seasons.  They 
differ  also  in  continental  and  marine  climates.  They 
differ  according  to  topography  and  cyclonic  and  anti- 
cyclonic  tracks.  The  oceans  in  the  south  temperate 
zone  have  a  constancy  of  non-periodic  cyclonic 
weather  changes  through  the  year  which  resembles 
only  faintly  that  over  the  oceans  of  the  northern  hemi- 
sphere. Winter  types  differ  little  from  summer 
types.  The  diurnal  control  is  never  very  strong. 
Stormy  weather  prevails  throughout  the  year,  al- 
though the  weather  changes  are  more  frequent  and 
stronger  in  the  colder  months. 

Climatic  Subdivisions.  From  whatever  point  of 
view  the  temperate  zones  be  considered,  it  is  clear  that 
there  are  fundamental  differences  between  the  north 
and  south  temperate.  The  latter  is  sufficiently  in- 
dividual to  be  given  a  place  by  itself.  The  marginal 
sub-tropical  belts  must  also  be  considered  as  a  separ- 
ate group  by  themselves.  The  north  temperate  zone 
as  a  whole  includes  large  areas  of  land,  stretching  over 
many  degrees  of  latitude,  as  well  as  of  water.  Hence 
it  embraces  so  remarkable  a  diversity  of  climates  that 
no  single  district  can  be  taken  as  typical  of  the  whole. 
Its  climate  has  been  called  "  a  crazy  quilt  of  patches." 
It  is  a  zone  of  marked  seasonal  variations  and  of 
great  extremes,  annual,  diurnal,  cyclonic.  The 
simplest  and  most  rational  scheme  for  a  classification 


CHARACTERISTICS  OF  ZONES— TEMPERATE  121 

of  these  climates  is  based  on  the  fundamental  differ- 
ences which  depend  upon  land  and  water,  upon  the 
prevailing  winds,  and  upon  altitude.  Thus  there  are 
the  ocean  areas  and  the  land  areas.  The  latter  are 
then  subdivided  into  western  (windward)  and  eastern 
(leeward)  coasts,  and  interiors.  Mountain  climates 
remain  as  a  separate  group. 

South  Temperate  Zone.  If  the  climate  of  the 
north  temperate  zone  is  "  a  crazy  quilt  of  patches," 
that  of  the  south  temperate  is  a  piece  of  fairly  uni- 
form texture  and  appearance  throughout.  This  is 
the  effect  of  the  large  ocean  surface.  The  whole 
meteorological  regime  is  more  uniform  than  in  the 
northern  zone.  Although  the  solar  climate  of  the 
southern  hemisphere  is  more  severe  than  that  of  the 
northern,  the  physical  climate  is  very  much  less  ex- 
treme. It  has  been  pointed  out  that  this  zone  may 
properly  be  called  "temperate";  that  its  tempera- 
ture changes  are  small;  its  prevailing  winds  are 
stronger  and  steadier  than  in  the  northern  hemisphere ; 
its  seasons  more  uniform;  its  weather  prevailingly 
stormier,  more  changeable,  and  more  under  cyclonic 
control.  The  uniformity  of  the  climatic  conditions 
over  the  far  southern  oceans  is  monotonously  unat- 
tractive. The  continental  areas  are  small,  and  de- 
velop toT  a  limited  degree  only  the  more  marked 
seasonal  and  diurnal  changes  which  are  characteristic 
of  lands  in  general.  The  summers  are  less  stormy 
than  the  winters,  but  even  the  summer  temperatures 
are  not  high.  Such  an  area  as  that  of  New  Zealand, 


122  CLIMATE 

with  its  mild  climate  and  fairly  regular  rains,  is  really 
at  the  margins  of  the  zone,  and  has  much  more 
favourable  conditions  than  do  the  islands  farther 
south.  These  islands,  in  the  heart  of  this  zone,  have 
dull,  cheerless,  and  inhospitable  climates,  with  snow 
sometimes  in  midsummer.  The  zone  enjoys  a  good 
reputation  for  healthfulness,  which  fact  has  been 
ascribed  chiefly  to  the  strong  and  active  air  move- 
ment, the  relatively  drier  air  than  in  corresponding 
northern  latitudes,  and  the  cool  summers.  It  must 
be  remembered,  also,  that  the  lands  are  mostly  in  the 
sub-tropical  belt,  which  possesses  peculiar  climate  ad- 
vantages, as  will  be  seen.  The  northern  oceans 
repeat,  in  a  much  modified  form,  many  of  the  charac- 
teristics of  the  south  temperate  oceans.  Except  to 
leeward  of  the  broad  lands,  the  northern  oceans  have 
the  conservative  features  typical  of  marine  climates 
the  world  over. 

Sub-tropical  Belts:  Mediterranean  Climates.  At 
the  tropical  margins  of  the  temperate  zones,  in  the 
latitudes  of  the  tropical  high  pressure  areas,  are 
the  so-called  sub-tropical  belts.  Far  enough  from  the 
equator  to  be  free  from  continued  high  temperatures, 
and  near  enough  to  it  to  be  spared  the  extreme  cold 
of  higher  latitudes,  these  transition  belts  are  among 
the  most  favoured  of  the  world.  Their  rainfall  re- 
gime is  alternately  that  of  the  westerlies  and  of  the 
trades.  They  are  thus  associated,  now  with  the  tem- 
perate, and  now  with  the  tropical  zones.  In  winter, 
the  equatorward  migration  of  the  great  pressure  and 


CHARACTERISTICS  OF  ZONES— TEMPERATE  123 

wind  systems  brings  these  latitudes  under  the  control 
of  the  westerlies,  whose  frequent  irregular  storms 
give  a  moderate  winter  precipitation.  These  winter 
rains  recall  the  winter  trade  rains  of  the  tropics, 
although  their  origin  is  different.  They  are  not 
steady  and  continuous,  but  are  separated  by  spells  of 
fine,  sunny  weather.  The  amounts  vary  greatly.1 

In  summer,  when  the  trades  are  extended  pole- 
wards by  the  outflowing  equatorward  winds  on  the 
eastern  side  of  the  ocean  highs,  mild,  dry,  and  nearly 
continuous  fair  weather  prevails,  with  general  north- 
erly winds. 

The  sub-tropical  belts  of  winter  rains  and  dry 
summers  are  not  very  clearly  defined.  They  do  not 
extend  continuously  around  the  world.  They  are 
mainly  limited  to  the  western  coasts  of  the  continents, 
and  to  the  islands  off  these  coasts,  in  latitudes  between 
about  28°  and  40°.  Their  degree  of  development 
and  their  importance  vary  in  different  longitudes. 
The  sub-tropical  belt  is  exceptionally  wide  in  the  east- 
ern hemisphere,  and  reaches  far  inland  there,  em- 
bracing the  countries  bordering  on  the  Mediterranean 
in  southern  Europe  and  northern  Africa,  including 
the  Azores  and  the  famous  Riviera,  and  then  extend- 
ing eastward  across  the  Dalmatian  coast  and  the 
southern  part  of  the  Balkan  peninsula  into  Syria, 
Mesopotamia,  Arabia  north  of  the  tropic,  Persia,  and 
adjacent  lands.  In  the  great  eastward  extension 


lln  round  numbers,   Lisbon   has   28.60   inches;    Madrid,   16.50; 
Algiers,  28.15;   Nice,  33.00;    Rome,  29.90;    Ragusa,   63.90. 


124  CLIMATE 

of  the  winter  rains  in  this  area,  the  development  of 
secondary  lows  over  the  Mediterranean  Sea  is  an  im- 
portant factor.  The  fact  that  the  Mediterranean 
countries  are  so  generally  included  in  this  belt  has  led 
to  the  use  of  the  name  "  Mediterranean  climates." 
Owing  to  the  great  irregularity  of  topography  and 
outline,  the  Mediterranean  province  embraces  many 
varieties  of  climate,  but  the  dominant  characteristics 
are  the  mild  temperatures,  except  on  the  higher  ele- 
vations, and  the  sub-tropical  rains. 

On  the  west  coasts  of  the  two  Americas,  the  sub- 
tropical belt  of  winter  rains  is  clearly  seen  in  Cali- 
fornia and  in  northern  Chile,  on  the  west  of  the  coast 
mountain  ranges.  Between  the  region  which  has  rain 
throughout  the  year  from  the  stormy  westerlies,  and 
the  districts  which  are  permanently  arid  under  the 
trades,  there  is  an  indefinite  belt  over  which  rains  fall 
in  winter.  In  southern  Africa,  which  is  controlled 
by  the  high  pressure  areas  of  the  South  Atlantic  and 
South  Indian  oceans,  the  south-western  coastal  belt 
has  winter  rains,  decreasing  to  the  north,  \vhile  the 
east  coast  and  adjoining  interior  have  summer  rains, 
from  the  south-east  trade.  There  is  sub-tropical  veg- 
etation on  the  south-east  coast,  and  a  cool,  dry  climate 
on  the  south-west  coast.  Southern  Australia  is  cli- 
matically similar  to  south  Africa.  In  summer,  the 
trades  give  rainfall  on  the  eastern  coast,  which  de- 
creases inland.  In  winter,  the  westerlies  give  mod- 
erate rains,  chiefly  on  the  south-western  coast. 
Northern  Chile,  California,  south-western  Australia, 


CHARACTERISTICS  OF  ZONES— TEMPERATE  125 

and  the  Cape  province  of  Africa  are  thus  all  in  the 
sub-tropical  belt. 


1000  THS 

200 

^S*** 

- 

ISO 

X 

-\ 

- 

100 
50 

WA 

y 

v 

^ 

^^^ 

" 

—  — 

***h. 

200 

• 

ISO 

^—  - 

~**^ 

. 

/** 

^^ 

100 

-  — 

—  •**> 

^ 

/ 

- 

50 
n 

• 

M. 

N 

X-, 

•  —  -* 

•*-^^*- 

^ 

' 

- 

FIG.  23.     MONTHLY  DISTRIBUTION  OF  RAINFALL:    SUB-TROPICAL 
WINTER  RAINS 

M:  Malta.     W.A:  Western  Australia 

The  sub-tropical  climates  follow  the  tropical  high 
pressure  belts  across  the  oceans,  but  they  do  not  re- 
tain their  distinctive  character  far  inland  from  the 
uest  coasts  of  the  continents  (except  in  the  Mediter- 
ranean case) ,  nor  on  the  east  coasts.  On  the  latter, 
summer-monsoons  and  the  occurrence  of  general  sum- 
mer rains  interfere,  as  in  eastern  Asia  and  in  Florida, 
and  to  some  extent  in  South  America  east  of  the 
Andes. 

Strictly  winter  rains,  with  a  maximum  in  Decem- 
ber or  in  June,  according  to  the  hemisphere,  are  typi- 


126  CLIMATE 

cal  of  the  coasts  and  islands  of  this  belt.  The  more 
continental  areas  have  a  tendency  to  spring  and 
autumn  rains.  The  rainy  and  dry  seasons  are  most 
marked  at  the  equatorward  margins  of  the  belt,  and 
thus  recall  the  tropical  characteristic  of  dry  and  wet, 
rather  than  cold  and  hot  seasons.  With  increasing 
latitude,  the  rain  is  more  evenly  distributed  through 
the  year,  the  summer  becoming  more  and  more  rainy 
until,  in  the  continental  interiors  of  the  higher  lati- 
tudes, the  summer  becomes  the  season  of  maximum 
rainfall.  The  monthly  distribution  of  rainfall  in  two 
sub-tropical  regions  is  shown  in  the  accompanying 
data  and  curves  (see  Fig.  23). 

ANNUAL    MARCH    OF    RAINFALL  I    SUB-TROPICAL   TYPE    (in    thoUS 

andths  of  the  annual  mean). 

Southern  Italy 
Western  Sicily 

Australia  Malta 

Latitude 32.3°  S.        About  38°  N. 

January 14  130 

February 18  93 

March 30  98 

April 64  75 

May 150  35 

June 183  23 

July 168  8 

August 166  28 

September 93  73 

October 59  133 

November 32  144 

December 23  160 

The  following  table  (from  Supan),  giving  the  sea- 
sonal distribution  of  rainfall  in  southern  Europe,  in 


CHARACTERISTICS  OF  ZONES— TEMPERATE  127 

percentages  of  the  annual  mean,  shows  very  clearly 
the  change  in  the  rainfall  season  in  going  from  north 
to  south.  In  the  northern  Tyrol,  the  normal  type  of 
central  Europe  prevails.  In  Sicily,  the  summer  is 
almost  rainless:  the  sub-tropical  type  is  fully 
developed. 

SEASONAL   DISTRIBUTION    OF   RAINFALL    IN    CENTRAL   AND    SOUTH- 
ERN EUROPE   (in  percentages  of  the  annual  mean). 

Winter  Spring   Summer  Autumn 

Northern  Tyrol  16  24  37  23 

Southern  Tyrol  14  26  28  32 

Po  Valley  20  26  24  30 

Central  Italy  25  24  17  34 

Southern  Italy  31  25  11  33 

Sicily  39  22                3  36 

Malta  48  14               2  36 

In  Alexandria  the  dry  season  lasts  nearly  eight 
months;  in  Palestine,  from  six  to  seven  months;  in 
Greece,  about  four  months. 

The  sub-tropical  rains  are  peculiarly  well  developed 
on  the  eastern  coast  of  the  Atlantic  Ocean,  and  are 
clearly  illustrated  in  the  accompanying  diagram, 
after  Supan  (see  Fig.  24). 

The  different  types  of  rainfall  are  as  follows: 

I.  ~North  of  lat.  40°  N.     Rain  throughout  the  year. 
II.     Lats.  40°— 27°  N.     Dry  in  summer    (sub-tropical 
rains). 

III.  Lats.  27°-19°  N.     Always  deficient  in  rainfall. 

IV.  Lats.     19°-7°     N.      Dry     in     winter      (tropical 

rains). 

V.     Lats.  7°-l°  N.     Always  rainy   (equatorial  belt). 


128 


CLIMATE 


VI.     Lats.  1°  N.-170  S.  Dry  in  winter  (tropical  rains). 
VII.     Lats.  17°-30°  S.     Always  dry. 
VIII.     Beyond  lat.  30°  S.     Dry  in  summer  (sub-tropical 

rains). 

(IX.     Always  rainy  on  the  oceans.     The  African  west 
coast  does  not  extend  into  this  zone.) 


Wint  e  r     Sumrrber 


Summer    Winter 

FIG.  24.    RAINY  AND  RAINLESS  ZONES  ON 
EASTERN   ATLANTIC   COAST 


The  winter  rains  which  migrate  equatorwrard  are 
separated  by  the  Sahara  from  the  equatorial  rains 
which  migrate  poleward.  An  unusually  extended 
migration  of  either  of  these  rain  belts  may  bring  them 


CHARACTERISTICS  OF  ZONES— TEMPERATE  129 

close  together,  leaving  but  a  small  part,  if  any,  of  the 
intervening  desert  actually  rainless.  The  Arabian 
desert  occupies  a  somewhat  similar  position.  Large 
variations  in  the  annual  rainfall,  and  droughts,  may 
be  expected  towards  the  equatorial  margins  of  the 
sub-tropical  belts.  Irrigation  is  practised  in  many 
places. 

TABLE    OF    MEAN    MONTHLY    TEMPERATURES    FOR    SELECTED    SUB- 
TROPICAL STATIONS.1 


Continental 

Insular 

Bagdad 

Cordoba 

Bermuda 

Auckland 

Lat. 

33°19'  N. 

31°25/  S. 

32°20/  N. 

36°50'  S. 

Long. 

44°26'  E. 

64°12'  W. 

64°43'  W. 

174°51/  E. 

Altitude 

39ft. 

1440  ft. 

148  ft. 

276  ft. 

January 

50.9° 

73.4° 

62.4° 

67.1° 

February 

53.1 

72.3 

61.9 

67.5 

March 

62.1 

68.4 

61.7 

65.5 

April 

69.3 

61.0 

64.4 

61.5 

May 

82.0 

54.5 

69.6 

56.7 

June 

89.6 

49.1 

74.8 

53.2 

July 

92.8 

50.0 

78.8 

51.8 

August 

92.7 

54.3 

80.1 

52.2 

September 

85.6 

58.6 

78.1 

54.5 

October 

76.5 

63.5 

73.4 

57.4 

November 

62.1 

68.5 

67.6 

60.3 

December 

52.5 

71.8 

63.7 

64.8 

Mean 

72.4 

62.1 

69.7 

59.4 

Range 

41.9 

24.3 

18.4 

15.7 

The  main  features  of  the  sub-tropical  rains  east  of 
the  Atlantic  are  repeated  on  the  Pacific  coasts  of  the 


1  Given  to  nearest  tenth  of  a  degree  Fahr. 

9 


130  CLIMATE 

two  Americas.  In  North  America,  the  rainfall  de- 
creases from  Alaska,  Washington,  and  northern  Ore- 
gon southwards  to  Lower  California,  and  the  length 
of  the  summer  dry  season  increases.  The  mean  an- 
nual rainfall  (1871-1901)  at  Neah  Bay,  Wash.,  is 
112.40  inches;  at  San  Francisco,  Cal.,  22.83  inches, 
and  at  San  Diego,  Cal.,  9.40  inches.  At  San  Diego, 
six  months  (May-October)  have  each  less  than  five 
per  cent,  of  the  annual  precipitation,  and  four  of 
these  have  one  per  cent.  The  southern  extremity  of 
Chile,  from  about  latitude  38°  S.  southward,  has 
heavy  rainfall  throughout  the  year  from  the  wester- 
lies, with  a  winter  maximum.  Northern  Chile  is  per- 
sistently dry.  In  the  intermediate  area  there  are 
winter  rains  and  dry  summers.  Neither  Africa  nor 
Australia  extends  far  enough  south  to  show  the  dif- 
ferent members  of  this  system  well.  New  Zealand 
is  almost  wholly  in  the  prevailing  westerly  belt. 
Northern  India  is  unique  in  having  summer  monsoon 
rains,  and  also  winter  rains  from  weak  cyclonic 
storms,  which  correspond  to  the  sub-tropical  winter 
rains. 

From  the  position  of  the  sub-tropical  belts  to  lee- 
ward of  the  oceans,  and  at  the  equatorial  margins  of 
the  temperate  zones,  it  follows  that  their  temperatures 
are  not  extreme.  Further,  the  protection  afforded 
by  mountain  ranges,  as  by  the  Alps  in  Europe  and 
the  Sierra  Nevada  in  the  United  States,  is  an  im- 
portant factor  in  keeping  out  extremes  of  winter  cold. 
The  annual  march,  and  ranges,  of  temperature  de- 


CHARACTERISTICS  OF  ZONES— TEMPERATE  131 

pend  upon  position  with  reference  to  continental  or 
marine  influences.  This  is  seen  in  the  accompanying 
data  and  curves  for  Bagdad,  Cordoba,  Bermuda,  and 
Auckland  (see  Fig.  25). 


J.  F.  M.  A.  M.  J.  J.  A.  S.  0.  l  D.  J. 


(QOO 


500 


J.  F.  M.  A.  M.  J.  J.  A.  5.  0.  N.  D.  J. 


FIG.   25.     ANNUAL  MARCH  OF  TEMPERATURE  FOR 

SELECTED  SUB-TROPICAL  STATIONS 

Bd:    Bagdad.        Ba:    Bermuda.        A:    Auckland. 

C:  Cordoba 

Autumn  is,  as  a  rule,  a  good  deal  warmer  than 
spring,  as  in  all  the  eastern  Mediterranean  basin,  the 
Canaries,  and  Madeira.  This  basin  is  particularly 


132  CLIMATE 

favoured  in  winter,  not  only  in  the  protection  against 
cold  afforded  by  the  mountains,  but  also  in  the  high 
temperature  of  the  sea  itself.  The  southern  Alpine 
valleys  and  the  Riviera  are  well  situated,  having  good 
protection  and  a  southern  exposure.  The  coldest 
month  usually  has  a  mean  temperature  well  above 
32°.  Mean  minimum  temperatures  of  about,  and 
somewhat  below,  freezing  occur  in  the  northern  por- 
tion of  the  district,1  and  in  the  more  continental  lo- 
calities minima  a  good  deal  lower  have  been  observed. 
(At  San  Diego,  Cal.,  the  absolute  minimum  is  32°; 
at  San  Francisco,  29°.)  Mean  maximum  tempera- 
tures of  about  95°  occur  in  northern  Italy,  and  of 
still  higher  degrees  in  the  southern  portions.  Some- 
what similar  conditions  exist  in  the  sub-tropical 
district  of  North  America.  Under  the  control  of 
passing  cyclonic  storm  areas,  hot  or  cold  winds,  which 
often  owe  some  of  their  special  characteristics  to  the 
topography,  bring  into  the  sub-tropical  belts,  from 
higher  or  lower  latitudes,  unseasonably  low  or  high 
temperatures.  These  winds  have  been  given  special 
names  (mistral,  sirocco,  bora,  chamsin,  leste,  leveche, 
pampero,  southerly  burster,  etc.) 

These  belts  enjoy  abundant  sunshine,  being  among 
the  least  cloudy  districts  in  the  world.  The  accom- 
panying data  and  curve,  giving  an  average  for  ten 
stations,  show  the  small  annual  amount  of  cloud,  the 
winter  maximum  and  the  marked  summer  minimum, 
in  a  typical  sub-tropical  climate.  (Fig.  26). 
iNice,  30.4°;  Rome,  25.7°;  Palermo,  32°;  Athens,  28.8°. 


CHARACTERISTICS  OF  ZONES— TEMPERATE  133 

MONTHLY    DISTRIBUTION    OF   CLOUDINESS    IN   A    SUB-TROPICAL 
CLIMATE    (EASTERN   MEDITERRANEAN,   LAT.  33.8°   N.) 

Jan.  Feb.  Mar.  Apr.  May  June  July  Aug.  Sept.  Oct.  Nov.  Dec.     Year 
4.9    4.6     3.8     3.7     2.8     1.3     1.1      1.3      1.8     2.5      4.0     4.7  3.0 

The  winter  rains  do  not  bring  continuously  over- 
cast skies;  and  it  has  been  well  said  that  the  problem 
of  securing  a  maximum  rainfall  with  a  maximum 
number  of  clear  days  has  been  solved  on  the  southern 
Alpine  slopes.  A  summer  month  with  a  mean 


\r\ 

,1 

F 

M 

A 

M 

J. 

J, 

A 

S 

0 

N 

0 

J, 

10 

10 

_ 

c: 

"•^x 

/ 

^ 

. 

^^-.^ 

--N 

Sy 

/ 

\ 

^ 

1 

n 

V 

1 

^-  — 

I 

n 

FIG.  26.    ANNUAL  MARCH  OF  CLOUDINESS  IN  A  SUB-TROPICAL  CLIMATE 
(Eastern  Mediterranean) 

cloudiness  of  0.1  is  not  exceptional  in  the  drier  parts 
of  the  sub-tropics.  The  winter  cloudiness  in  northern 
Italy  is  5.0  to  6.0;  in  summer,  3.0  to  4.0.  Cairo 
has  an  annual  mean  of  1.9,  and  in  June  it  has 
0.8.  Biskra,  on  the  northern  margin  of  the  Sahara, 
has  264  clear  days.  In  the  central  valley  of  Cali- 


134  CLIMATE 

fornia,  the  number  of  clear  days  is  similarly  very 
large. 

With  prevailingly  fair  skies,  even  temperatures,  and 
moderate  rainfall,  the  sub-tropical  belts  possess  many 
climatic  advantages  which  fit  them  for  health  resorts. 
The  long  list  of  well-known  resorts  on  the  Mediter- 
ranean coast,  and  the  shorter  list  for  California,  bear 
witness  to  this  fact. 

North  Temperate  Zone:  West  Coasts.  Marine 
climatic  types  are  carried  by  the  prevailing  wester- 
lies on  to  the  western  coasts  of  the  continents,  giving 
them  mild  winters  and  cool  summers,  abundant  rain- 
fall and  a  high  degree  of  cloudiness  and  relative 
humidity.  North-western  Europe  is  particularly 
favoured  because  of  the  remarkably  high  tempera- 
tures of  the  North  Atlantic  Ocean,  and  because  of  the 
influence  of  the  winds  controlled  by  the  low  pressure 
area  off  Iceland.  In  January,  north-western  Europe 
has  temperatures  from  20°  to  40°  in  excess  of  the 
normal  for  the  latitude.  The  north-western  coast  of 
North  America  has  temperatures  more  than  10°  too 
warm  for  the  latitude.  January  means  of  40°  to  50° 
in  the  British  Isles  and  on  the  northern  French  coast 
occur  in  the  same  latitudes  as  those  of  0°  and  10°  in 
the  far  interior  of  Asia.  In  July,  means  of  60°  to 
70°  in  the  former  contrast  with  70°  and  80°  in  the  lat- 
ter districts.  The  conditions  are  somewhat  similar 
in  North  America.  Along  the  western  coasts  of 
North  America  and  of  Europe  the  mean  annual 
ranges  are  under  25°, — actually  no  greater  than  some 


J.  F.  M.  A.  M.  J.  J.  A.  S.  0.  N.  D.  J. 


FIG.  27.  ANNUAL  MARCH  OF 
TEMPERATURE  FOR  SELECTED 
STATIONS  IN  THE  TEMPERATE 

ZONES 

S.  I:  Scilly  Isles.  P:  Prague.  C: 
Charcovv.  S:  Semipalatinsk.  K; 
Kiakhta.  B:  Blagoweschtschensk. 
Sa:  Sakhalin.  T:  Thorshavn. 
Y:  Yakutsk 


135 


136 


CLIMATE 


of  those  within  the  tropics.  Irregular  cyclonic  tem- 
perature changes  are,  however,  marked  in  the  tem- 
perate zone,  while  absent  in  the  tropics.  The  data 
and  curves  for  the  Scilly  Isles  and  for  Thorshavn, 
Faroe  Islands,  illustrate  the  insular  type  of  temper- 
ature on  the  west  coasts  (see  Fig.  27).  In  the 
Faroes  the  mean  maximum  is  65.1°,  and  the  mean 
minimum  16°.  It  will  be  noted  that  the  poleward 
decrease  in  the  mean  annual  and  the  mean  winter 
temperatures  is  very  slow  between  latitudes  50°  and 
62°  N.  on  the  west  coast  of  Europe. 

TABLE    OP    MEAN    MONTHLY    TEMPERATURES    FOR    SELECTED    STA- 
TIONS  IN   THE   TEMPERATE   ZONES. 


Along  lat.  50°  N. 

At  lat.  62°N. 

West 
Coast 

Continental 

East 
Coast 

Insular 

Conti- 
nental 

Scilly 
Isles 

Prague 

Charcow 

Semi- 
paja- 

tinsk 

Kiakh- 
ta 

Blago- 
wescht- 
schensk 

Sakha- 
lin 

Thors- 
havn, 
Faroe 
Isles 

Yakutsk, 
E.  Si- 
beria 

Lat. 

49°55' 

50°5' 

50°2' 

50°24' 

50°21' 

50°  15' 

50°50' 

62°2' 

62°!' 

Long. 

6°20'  W. 

14°26'  E. 

36°11' 

80°13' 

106°31' 

127°38' 

142°7'  E. 

6°44'  W. 

129°43'E 

Alt.  (ft.) 

98.4 

662.7 

413.4 

593.8 

2526 

360.9 

180.4 

29.5 

328.1 

Jan. 

45.7° 

29.8° 

16.5° 

0.5° 

-15.9° 

-13.9° 

-0.4° 

37.8° 

-45.2° 

Feb. 

45.7 

32.0 

22.1 

1.8 

-5.4 

-3.3 

5.0 

38.1 

-35.0 

March 

46.0 

37.8 

29.3 

14.4 

16.9 

14.4 

15.8 

37.8 

-10.7 

April 

48.7 

47.3 

44.8 

38.3 

34.3 

34.7 

31.1 

41.9 

15.1 

May 

52.5 

55.9 

58.8 

57.2 

48.7 

49.6 

41.4 

45.0 

40.3 

June 

57.9 

63.3 

65.1 

68.0 

63.1 

63.7 

50.7 

49.5 

58.5 

July 

60.8 

66.7 

69.6 

72.0 

66.4 

70.5 

60.3 

51.4 

65.8 

Aug. 

61.2 

65.3 

66.4 

67.3 

61.7 

65.8 

62.2 

51.3 

59.7 

Sept. 

58.6 

58.8 

56.1 

54.9 

48.0 

53.2 

53.6 

48.7 

42.3 

Oct. 

54.0 

48.7 

45.5 

38.1 

32.0 

34.2 

39.6 

43.9 

15.8 

Nov. 

49.6 

37.6 

33.8 

20.1 

11.8 

9.7 

22.5 

40.6 

-21.3 

Dec. 

47.3 

31.3 

23.2 

6.1 

-2.7 

-9.2 

7.3 

38.1 

-41.1 

Year 

52.3 

47.9 

44.3 

36.5 

29.9 

30.8 

32.4 

43.7 

12.0 

Range 

15.5 

36.9 

53.1 

71.5 

82.3 

84.4 

62.6 

13.6 

111.0 

CHARACTERISTICS  OF  ZONES— TEMPERATE  137 


MONTHLY     DISTRIBUTION     OF     RAINFALL     (iN     THOUSANDTHS     OF 
THE    ANNUAL    MEAN).      TEMPERATE    ZONE. 


Continental  Summer  Rains 

Coast  Rains 

Moderate 

Marked 
Summer 
Maximum 

Uniform 
Distribution 

Fall  and 
Winter  Rains 

Central 

Atlantic 

Europe 

Northern 

Coast, 

North-west 

North  of 

Asia 

North 

Europe 

Alps 

America 

Lat. 

About  50°  N. 

About  55°  N. 

About  40°  N. 

About  60°  N. 

January 

57 

20 

84 

100 

February 

56 

17 

77 

80 

March 

68 

18 

85 

72 

April 

71 

35 

70 

56 

May 

92 

75 

80 

58 

June 

115 

235 

81 

64 

July 

121 

215 

96 

70 

August 

117 

122 

87 

80 

September 

82 

133 

84 

102 

October 

75 

58 

91 

110 

November 

74 

40 

86 

102 

December 

72 

32 

79 

106 

The  monthly  distribution  of  rainfall,  with  the 
marked  maximum  in  the  fall  and  winter  which  is 
characteristic  of  the  marine  regime,  is  illustrated  in 
the  last  column  of  the  table  above,  for  north-western 
Europe^  and  in  the  corresponding  curve  (see  Fig. 
28). 

On  the  northern  Pacific  coast  of  North  America, 
the  distribution  is  similar.  Thus  at  Olympia,  Wash- 
ington, there  is  a  distinct  cold  season  maximum,  as 
appears  in  the  following  data: 


138  CLIMATE 

MONTHLY    DISTRIBUTION    OF    RAINFALL    AT    OLYMPIA,    WASHING- 
TON   (IN    THOUSANDTHS    OF   THE    ANNUAL    MEAN). 

January     159 

February    135 

March    95 

April    65 

May    44 

June    31 

July    13 

August    13 

September   53 

October    86 

November    124 

December    182 

In  the  southern  hemisphere,  the  western  coasts  of 
southern  South  America,  Tasmania,  and  New  Zea- 
land show  the  same  type. 

The  cloudiness  and  relative  humidity  average  high 
on  western  coasts,  with  the  maximum  in  the  colder 
season.  The  difference  in  general  rainfall  conditions 
between  the  west  coast,  typified  by  the  exaggerated 
case  of  Valentia,  in  south-western  Ireland,  and  the 
Mediterranean,  is  seen  in  the  number  of  rainy  days 
in  each  district.  Valentia  has  nearly  250.  In  the 
Mediterranean,  they  may  be  set  down  as  about  100, 
in  round  numbers. 

The  west  coasts,  therefore,  including  the  important 
climatic  province  of  western  Europe,  and  the  coast 
provinces  of  north-western  North  America,  New 
Zealand,  and  southern  Chile,  have,  as  a  whole,  mild 
winters,  equable  temperatures,  small  ranges,  and 


'CHARACTERISTICS  OF  ZONES—  TEMPERATE  139 


abundant  rainfall,  fairly  well  distributed  through  the 
year.  The  summers  are  relatively  cool,  especially  on 
the  Chilean  coast. 


1000 THS 

150 
100 
50 

0 

250 

200 

150 

100 

50 

0 

100 
50 

0 

150 
100 
50 

0 


J.  F.  M.  A   M.  J.  J.  A.  S.  0.  N.  D.  J. 


J.  F.  M.  A.  M.  J.  J.  A.  S.  0.  N.  D. 


FIG.   28.      ANNUAL  MARCH  OF  RAINFALL:  TEMPERATE  ZONES 
C   E:  Central  Europe.      A:  Northern  Asia.      N.  A:  Atlantic  Coast  of 
North  America,     N.  W.E:  Northwest  Europe 

Continental  Interiors.  The  equable  climate  of  the 
western  coasts  changes,  gradually  or  suddenly,  into 
the  more  extreme  climates  of  the  interiors.  In 
Europe,  where  no  high  mountain  ranges  intervene, 


140  CLIMATE 

the  transition  is  gradual,  and  broad  stretches  of  coun- 
try have  the  benefits  of  the  tempering  influence  of  the 
Atlantic.  In  North  America,  the  change  is  abrupt, 
and  comes  on  crossing  the  lofty  western  mountain 
barrier.  The  data  in  the  table  on  page  136,  and  the 
corresponding  curves  in  Fig.  27,  illustrate  well  the 
gradually  increasing  severity  of  the  climate  with  in- 
creasing distance  inland  in  Eurasia.  Central  Europe 
is  seen  to  lie  between  the  modified  marine  climate  of 
the  west  coast  and  the  continental  conditions  of 
Russia  and  Siberia.  Its  mean  temperatures  do  not 
differ  very  much  from  those  on  the  coast,  but  the 
seasons  are  more  sharply  contrasted. 

The  continental  interiors  of  the  north  temperate 
zone  have  the  greatest  extremes  in  the  world.  To- 
wards the  Arctic  circle,  the  winters  are  extremely  se- 
vere, and  January  mean  temperatures  of  -—10°  and 
—20°  occur  over  considerable  areas.  At  the  cold  pole 
of  northern  Siberia  a  January  mean  of  —60°  is  found. 
Mean  minimum  temperatures  of  — 40°  occur  in  the 
area  from  eastern  Russia,  over  Siberia  and  down  to 
about  latitude  50°  N.  At  Verkhoyansk,  an  im- 
portant town  just  beyond  the  Arctic  circle,  the  ab- 
solute minimum  is  below  —90°.  Over  no  small  part 
of  Siberia  minimum  temperatures  below  — 70°  may 
be  looked  for  every  winter.  Thorshavn  and  Yak- 
utsk (see  table  on  page  136)  are  excellent  examples 
of  the  temperature  differences  along  the  same  lati- 
tude line.  The  winter  in  this  interior  region  is  domi- 
nated by  a  marked  high  pressure.  The  weather  is 


CHARACTERISTICS  OF  ZONES— TEMPERATE  141 

prevailingly  clear  and  calm.  The  ground  below  a 
slight  depth  is  frozen  the  year  around,  over  wide 
areas.  The  moderate  snowfall  is  sufficient,  with  the 
continued  cold,  to  make  sleighing  possible  for  im- 
mense stretches  all  over  the  country.  The  frozen 
rivers  can  be  crossed  without  bridges.  This  unifying 
influence,  of  easy  winter  communication,  has  been 
most  important  in  Russian  history,  as  Leroy-Beau- 
lieu  has  pointed  out.  The  extremely  low  tempera- 
tures are  not  disagreeable  except  when  the  steppes 
are  swept  by  icy  storm  winds  (buran,  purga), 
carrying  loose  snow,  and  often  resulting  in  loss  of 
life/ 

In  the  North  American  interior,  the  winter  cold  is 
somewhat  less  severe.  The  lowest  January  mean 
temperatures  are  —30°,  in  the  extreme  northern  por- 
tion of  the  continent.  Mean  annual  minima  of  — 40° 
occur  down  into  the  northern  interior  portion  of  the 
United  States.  The  lowest  is  about  — 60°,  near  Great 
Bear  Lake,  with  an  absolute  minimum  of  about  — 72°. 
North  American  winter  weather  in  middle  latitudes 
is  often  interrupted  by  cyclones,  which,  under  the 
steep  poleward  temperature  gradient  then  prevail- 
ing, cause  frequent,  marked,  and  sudden  changes  in 
wind  direction  and  temperature  over  the  central  and 
eastern  United  States.  Cold  waves  and  warm  waves 
are  common,  and  blizzards  resemble  the  buran  or 
purga  of  Russia  and  Siberia.  With  cold  northerly 
winds,  temperatures  below  freezing  are  carried  far 
south  towards  the  tropic.  The  January  mean  tern- 


142  CLIMATE 

peratures  in  the  southern  portions  of  the  continental 
interiors  average  about  50°  or  60°. 

In  summer,  the  northern  continental  interiors  are 
warm,  with  July  means  of  60°  and  thereabout. 
These  temperatures  are  not  much  higher  than  those 
on  the  west  coasts,  but  as  the  northern  interior  win- 
ters are  much  colder  than  those  on  the  coasts,  the  in- 
terior ranges  are  very  large.  The  mean  annual 
extreme  ranges  exceed  150°  in  northern  North 
America  and  170°  in  Siberia.  Mean  maximum  tem- 
peratures of  85°  occur  beyond  the  Arctic  circle  in 
north-eastern  Siberia,  and  beyond  latitude  60°  in 
North  America.  In  spite  of  the  extreme  winter  cold, 
agriculture  extends  remarkably  far  north  in  these 
regions,  because  of  the  warm,  though  short,  summers, 
with  favourable  rainfall  distribution.  The  July 
isotherm  of  50°  is  about  the  northern  limit  of  tree 
growth.  Beyond  a  zone  of  stunted  tree  growth, 
comes  the  tundra.  The  summer  heat  is  sufficient  to 
thaw  the  upper  surface  of  the  frozen  ground,  and 
vegetation  prospers  for  its  short  season.  At  this 
time,  great  stretches  of  flat  surface  become  swamps. 
The  southern  interiors  have  torrid  heat  in  summer, 
temperatures  of  over  90°  being  recorded  in  the  south- 
western United  States  and  in  southern  Asia.  In 
these  districts  the  diurnal  ranges  of  temperature  are 
very  large,  often  exceeding  40°,  and  the  mean 
maxima  exceed  110°. 

In  South  America,  the  interior  of  Argentina  has 
moderate  mean  annual  ranges  (20°-30°)  ;  the  mean 


CHARACTERISTICS  OF  ZONES— TEMPERATE  143 

maxima  reach  95°-100°  and  even  higher,  and  the 
mean  minima  fall  below  23°.  The  west  coast  has 
smaller  ranges  (less  than  20°) ;  lower  mean  maxima 
(77°-86°),  and  higher  mean  minima  (32°-23°). 

The  winter  maximum  rainfall  of  the  west  coasts 
becomes  a  summer  maximum  in  the  interiors.  The 
change  is  gradual  in  Europe,  as  is  the  change  in  tem- 
perature, but  more  sudden  in  North  America.  The 
curves  for  central  Europe  and  for  northern  Asia  (see 
Fig.  28)  illustrate  these  continental  summer  rains. 
The  summer  maximum  becomes  more  marked  with 
the  increasing  continental  character  of  the  climate. 
Thus,  while  June  to  August  in  central  Europe  supply 
about  thirty-five  per  cent,  of  the  annual  precipita- 
tion, in  northern  Asia,  excluding  the  coast,  they  give 
nearly  sixty  per  cent.  The  rains  of  Asia  are  actually 
comparable,  in  relative  intensity,  at  their  maximum, 
with  the  rains  of  the  tropics.  In  Bengal,  e.  g.,  June 
to  August  give  only  fifty-seven  per  cent,  of  the 
annual  rainfall.  The  winter  dry  season  of  Asia  is, 
however,  very  different  from  a  tropical  dry  season,  be- 
cause of  the  difference  in  conditions  of  vegetation  and 
of  snow  cover.  In  North  America,  Nebraska,  a  state 
which  is  typical  of  a  considerable  district  of  summer 
rains,  receives  about  sixty  per  cent,  of  the  annual 
rainfall  in  the  months  of  April,  May,  June,  and 
July. 

The  change  in  rainfall  season  with  increasing  dis- 
tance from  the  Atlantic  Ocean  in  Eurasia  is  well 
brought  out  by  Supan  in  the  following  table: 


144  CLIMATE 

TABLE      SHOWING      SEASONAL      DISTRIBUTION      OF      RAINFALL      IN 
EURASIA    (IN   PERCENTAGES   OF   THE    ANNUAL   MEAN). 

Winter  Spring    Summer  Autumn 

Ireland  28  21  24  27 

Western  England  28  19  24  29 

Eastern  England  23  19  28  30 

North-western  Germany  23  22  31  24 

Central  Germany  20  23  34  23 

Eastern  Germany  19  22  37  22 

Western  Russia  16  21  39  24 

Central  Russia  16  22  37  25 

Western  Siberia  13  13  42  32 

Eastern  Siberia  9  12  58  21 

There  is  also  a  well-marked  decrease  in  the  amount 
of  rainfall  inland.  In  western  Europe,  the  rainfall 
averages  20-30  inches,  with  much  larger  amounts 
(reaching  80-100  inches  and  even  more)  on  the 
bold  west  coasts,  as  in  the  British  Isles  and  Scan- 
dinavia, where  the  moist  Atlantic  winds  are  deflected 
upwards,  and  also  locally  on  mountain  ranges,  as  on 
the  Alps.  There  are  small  rainfalls  (below  20 
inches)  in  eastern  Scandinavia  and  on  the  Iberian 
peninsula.  Eastern  Europe  has  generally  less  than 
20  inches;  western  Siberia  about  15  inches,  and  east- 
ern Siberia  about  10  inches.  In  the  southern 
part  of  the  great  overgrown  continent  of  Asia,  an  ex- 
tended region  of  steppes  and  deserts,  too  far  from 
the  sea  to  receive  sufficient  precipitation,  shut  in  by 
mountains,  and  controlled  in  summer  by  drying 
northerly  winds,  receives  less  than  10  inches  a  year, 
and  in  places  less  than  5  inches.  In  this  interior 
district  of  Asia,  population  is  inevitably  small,  and 
suffers  under  a  condition  of  hopeless  aridity. 


CHARACTERISTICS  OF  ZONES— TEMPERATE  145 

The  North  American  interior  has  more  favourable 
rainfall  conditions  than  Asia,  because  the  former 
continent  is  narrower.  The  heavy  rainfalls  on  the 
western  slopes  of  the  Pacific  coast  mountains 
correspond,  in  a  general  way,  to  those  on  the  west 
coast  of  Europe,  although  they  are  heavier  (over  100 
inches  at  a  maximum) .  The  close  proximity  of  the 
mountains  to  the  Pacific,  however,  involves  a  much 
more  rapid  decrease  of  rainfall  inland  than  is  the  case 
in  Europe,  as  may  be  seen  by  comparing  the  isohyetal 
lines  in  the  two  cases.  The  rain-shadow  influence  of 
the  Pacific  coast  Cordilleras  extends  about  half-way 
across  the  continent.  A  considerable  interior  region 
is  left  with  deficient  rainfall  (less  than  10  inches)  in 
the  south-west.  The  eastern  portion  of  the  continent 
is  freely  open  to  the  Atlantic  and  the  Gulf  of  Mexico, 
so  that  moist  cyclonic  winds  have  free  access,  and 
rainfalls  of  over  20  inches  are  found  everywhere  east 
of  the  100th  meridian.  These  conditions  are  much 
more  favourable  than  those  in  eastern  Asia.  The 
greater  part  of  the  interior  of  North  America  has  the 
usual  warm-season  rains.  In  the  interior  basin,  be- 
tween the  Rocky  and  Sierra  Nevada  mountains,  the 
higher  plateaus  and  mountains  receive  much  more 
rain  than  the  desert  lowlands.  Forests  grow  on  the 
higher  elevations,  while  irrigation  is  necessary  for 
agriculture  on  the  lowlands.  The  rainfall  here  comes 
chiefly  from  thunder-storms. 

In  southern  South  America,  the  narrow  Pacific 
slope  has  heavy  rainfall  (over  80  inches).  East  of 


146  CLIMATE 

the  Andes  the  plains  are  dry  (mostly  less  than  10 
inches).  The  southern  part  of  the  continent  is  very 
narrow,  and  is  open  to  the  east.  It  is  also  more  open 
to  the  west  than  is  the  country  farther  north,  owing 
to  the  decreasing  height  of  the  mountains  southward. 
Hence  the  rainfall  increases  somewhat  to  the  south, 
coming  in  connection  with  passing  cyclones.  Tas- 
mania and  New  Zealand  have  most  rain  on  their 
western  slopes. 

In  a  typical  continental  climate,  the  winter,  except 
for  radiation  fogs,  is  very  clear,  and  the  summer  is 
the  cloudiest  season,  as  is  well  shown  in  the  follow- 
ing data  and  curve  for  eastern  Asia.  In  a  more 
moderate  continental  climate,  such  as  that  of  central 
Europe,  and  much  of  the  United  States,  the  winter 
is  the  cloudiest  season  (see  Fig.  29). 

MONTHLY      DISTRIBUTION      OP      CLOUDINESS       IN       CONTINENTAL 

CLIMATES. 

I.  Eastern  Asia.  10  stations.  Lat.  56.5°  N.     Long.  115°  E. 
Jan.  Feb.  Mar.  Apr.  May  June  July  Aug.  Sept.  Oct.  Nov.  Dec.     Year. 

3.1     3.4     3.9     4.7     5.7     5.6     6.2     6.0     5.5      5.4      4.8   4.2  4.9 

II.     Central  Europe.     Hungarian  Plain.     Lat.  47°   N. 
Jan.  Feb.  Mar.  Apr.  May  June  July  Aug.  Sept.  Oct.  Nov.  Dec.       Year. 

6.5     5.9     5.7     5.6     5.4     5.3     4.4     4.2     4.6      5.8     6.6     6.9  5.6 

In  the  first  case,  the  mean  cloudiness  is  small;  in 
the  second,  there  is  a  good  deal  of  cloud  all  the  year 
around. 

The  vast  continental  interiors,  whose  climatic 
features  have  here  been  outlined,  can  obviously  be 


CHARACTERISTICS  OF  ZONES— TEMPERATE  147 

subdivided    into    smaller    climatic    provinces    almost 
indefinitely,  as  pointed  out  in  Chapter  III. 


IU 

9 
8 
7 
6 
5 
4 
3 
2 
1 
n 

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9 
8 
7 
6 
5 
4 
3 
2 
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^^ 

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vft. 

FIG.  29.     ANNUAL  MARCH  OF  CLOUDINESS  IN  CONTINENTAL  AND 
MOUNTAIN  CLIMATES  :  TEMPERATE  ZONES. 

E  :  Central  Europe.     A  :   Eastern  Asia.     M  :  Mountain 

East  Coasts.  The  prevailing  winds  carry  the  ma- 
rine climate  of  the  oceans  on  to  the  western  coasts  of 
the  temperate  zone  lands.  They  also  carry  the  con- 
tinental climates  of  the  interiors  off  over  the  eastern 
coasts  of  these  same  lands,  and  even  for  some  distance 
on  to  the  adjacent  oceans.  The  east  coasts,  therefore, 
have  continental  climates,  with  modifications  result- 
ing from  the  presence  of  the  oceans  to  leeward,  and 
are  necessarily  separated  from  the  west  coasts,  with 
which  they  have  little  in  common.  On  the  west  coasts 
of  the  north  temperate  lands  the  isotherms  are  far 
apart.  On  the  east  coasts,  they  are  crowded  together. 
The  east  coasts  share  with  the  interiors  large  annual 


US  CLIMATE 

and  cyclonic  ranges  of  temperature.  At  latitude  55° 
N.,  for  example,  the  east  coast  of  Asia  has  a  mean 
annual  range  which  is  four  times  as  large  as  that  of 
the  west  coast.  A  glance  at  the  isothermal  maps  of 
the  world  will  show  at  once  how  favoured,  because 
of  its  position  to  leeward  of  the  warm  North  Atlantic 
waters,  is  western  Europe  as  compared  with  eastern 
North  America.  A  similar  contrast,  less  marked,  is 
seen  in  eastern  Asia  and  western  North  America. 
In  eastern  Asia,  there  is  some  protection,  by  the  coast 
mountains,  against  the  extreme  cold  of  the  interior, 
but  in  North  America  there  is  no  such  barrier,  and 
severe  cold  winds  sweep  across  the  Atlantic  coast 
states,  even  far  to  the  south.  Owing  to  the  prevail- 
ing offshore  winds,  the  oceans  to  leeward  have  rela- 
tively little  effect.  In  the  north-east,  the  cold  water 
is  effective  in  giving  cooler  summers  than  farther 
south. 

As  already  noted,  the  rainfall  increases  from  the 
interiors  towards  the  east  coasts.  In  North  America, 
the  distribution  through  the  year  is  very  uniform, 
with  some  tendency  to  a  summer  maximum,  as  in  the 
interior  (see  Fig.  28). 

In  eastern  Asia  the  winters  are  relatively  dry  and 
clear,  under  the  influence  of  the  cold  offshore  mon- 
soon, and  the  summers  are  warm  and  rainy,  with  the 
northward  extension  of  the  south-east  monsoon,  which 
reaches  as  far  as  lat.  60°  N.  The  summer  maximum 
of  rainfall  on  this  coast  is  clearly  shown  in  the  follow- 
ing data  (Trabert) : 


CHARACTERISTICS  OF  ZONES— TEMPERATE  149 

MONTHLY    DISTRIBUTION    OF     RAINFALL.       EAST     COAST    OF     ASIA. 
(IN    PERCENTAGES    OF    ANNUAL     MEAN). 

Jan.  Feb.  Mar.  Apr.  May  June  July  Aug.  Sept.  Oct.  Nov.  Dec.    Year. 
22        3        6        8       10     12       21      16       11       6        3     19.3  ins. 

Rainfalls  of  40  inches  are  found  on  the  east 
coasts  of  Korea,  Kamchatka,  and  Japan,  while  in 
North  America,  which  is  more  open,  they  reach 
farther  inland.  Japan,  although  occupying  an  in- 
sular position,  has  a  modified  continental,  rather  than 
a  marine  climate.  The  winter  monsoon,  after  cross- 
ing the  water,  gives  abundant  rain  on  the  western 
coast,  while  the  winter  is  relatively  dry  on  the  lee  of 
the  mountains,  on  the  east.  Japan  has  smaller  tem- 
perature ranges  than  the  mainland. 

Mountain  Climates.  The  mountain  climates  of 
the  temperate  zone  have  the  usual  characteristics 
which  are  associated  with  altitude  everywhere.  If 
the  altitude  is  sufficiently  great,  the  decreased  tem- 
perature gives  mountains  a  polar  climate,  with  the 
difference  that  the  summers  are  relatively  cool,  while 
the  winters  are  mild,  owing  to  inversions  of  tempera- 
ture in  anticyclonic  weather.  Hence  the  annual 
ranges  are  smaller  than  over  lowlands.  At  such 
times  of  inversion,  the  mountain  tops  often  appear 
as  local  areas  of  higher  temperatures  in  a  general 
region  of  colder  air  over  the  valleys  and  lowlands. 
The  increased  intensity  of  insolation  aloft  is  an  im- 
portant factor  in  giving  certain  mountain  resorts 
their  deserved  popularity  in  winter  (e.  g.,  Davos  and 


150  CLIMATE 

Meran).  Of  Meran  it  has  been  well  said  that  from 
December  to  March  the  nights  are  winter,  but  the 
days  are  mild  spring.  Mountains  provoke  rainfall, 
even  in  arid  continental  interiors,  and  thus  we  have 
well- forested  plateaus  and  mountain  slopes  rising 
above  desert  lowlands.  The  diurnal  ascending  air 
currents  of  summer  usually  give  mountains  their 
maximum  cloudiness  and  highest  relative  humidity 
in  the  warmer  months,  while  winter  is  the  drier  and 
clearer  season.  This  is  shown  in  the  data  below  (see 
Fig.  29). 

MONTHLY  DISTRIBUTION  OF  CLOUDINESS.  MOUNTAIN  CLIMATE. 
(CENTRAL  EUROPE.  ALPINE  SUMMITS.  8500  FT.  LAT.  47°  N. 

SEVEN    STATIONS.) 

Jan.  Feb.  Mar.  Apr.  May  June  July  Aug.  Sept.  Oct.  Nov.  Dec.  Year. 
5.0  5.3  6.0  6.5  7.0  6.7  6.1  5.8  6.0  6.0  5.5  5.1  5.9 

The  clouds  of  winter  are  low;  those  of  summer 
are  higher.  Hence  the  annual  march  of  cloudiness 
on  mountains  is  usually  the  opposite  of  that  on 
lowlands. 


CHAPTER  VI 

THE  CHARACTERISTICS  OF  THE  ZONES:  III.— THE 
POLAR  ZONES 


General:  Relation  to  Man,  Animals,  and  Plants — Temperature — 
Pressure  and  Winds — Rain  and  Snow — Humidity,  Cloudiness, 
and  Fog — Cyclones  and  Weather — Twilight  and  Optical 
Phenomena — Physiological  Effects. 


General:  Relation  to  Man,  Animals,  and  Plants. 
The  temperate  zones  merge  into  the  polar  zones  at 
the  Arctic  and  Antarctic  circles  or,  if  temperature 
is  used  as  the  basis  of  classification,  at  the  isotherms 
of  50°  for  the  warmest  month,  as  suggested  by  Su- 
pan.  The  frequent  use  of  maps  on  the  Mercator 
projection  tends  to  give  us  an  exaggerated  idea  of 
the  size  of  the  polar  zones.  When  limited  by  the  polar 
circles,  these  zones  occupy  but  0.08  of  the  surface  of 
each  hemisphere,  the  whole  area  being  1.00.  As- 
tronomically they  are  distinguished  by  the  fact  that 
at  all  places  within  them  the  sun  is  above  the  horizon 
at  least  one  full  twenty-four  hours  each  year,  and  be- 
low it  the  same  length  of  time.  This  longer  or  shorter 
absence  of  the  sun  gives  the  climate  a  peculiar  char- 
acter, not  found  elsewhere.  At  the  poles,  the  day 


152  CLIMATE 

and  the  year  are  alike.  These  zones  obviously  have 
the  most  oblique  insolation. 

Our  knowledge  of  polar  climatology  has  advanced 
very  rapidly  in  the  last  two  decades.  The  fragmen- 
tary records  of  the  earlier  expeditions  gave  scattering 
information  about  the  weather.  The  longer  and 
more  complete  records  of  recent  expeditions  give 
much  more  accurate  and  satisfactory  results.  It  is 
now  becoming  possible  to  see  more  clearly  what  the 
climatic  conditions  really  are.  But  no  satisfactory 
presentation  of  polar  climatology  is  yet  possible. 
We  are  still  dealing  with  the  meteorology  of  the 
polar  zones,  rather  than  with  their  climates.  More 
is  known  of  the  Arctic  than  of  the  Antarctic.  The 
admirable  report,  by  the  late  Dr.  Henrik  Mohn,  on 
the  results  of  the  Nansen  North  Polar  expedition,  em- 
bracing three  years'  observations,  discussed  with  great 
care,  and  well  illustrated  by  curves  and  charts,  is  a 
monumental  piece  of  work.  From  the  Antarctic,  in 
recent  years,  English,  Scotch,  French,  Swedish,  Bel- 
gian, Norwegian,  Australian,  and  German  expedi- 
tions have  brought  back  a  great  wealth  of  valuable 
meteorological  material,  the  observations  in  several 
cases  covering  a  whole  year  and  also  including  records 
obtained  by  means  of  balloons.  These  data,  which 
have  been  critically  studied  and  compared,  have  made 
possible  the  construction  of  meteorological  charts, 
and  even  of  daily  weather  maps,  for  the  far  southern 
latitudes,  hitherto  largely  a  blank  on  our  maps. 

Beyond  the  isotherm  of  50°  for  the  warmest  month, 


CHARACTERISTICS   OF  ZONES— POLAR       153 

forest  trees  and  cereals  do  not  grow.  In  the  northern 
hemisphere  this  line  is  well  north  of  the  Arctic  circle 
in  the  continental  climate  of  Asia,  and  north  of  it  in 
north-western  North  America.  It  is  north  of  it  also 
in  northern  Scandinavia,  but  falls  well  south  in  east- 
ern British  America,  Labrador,  and  Greenland,  and 
also  in  the  North  Pacific  Ocean.  In  the  southern 
hemisphere  this  isotherm  crosses  the  southern  extrem- 
ity of  South  America,  and  runs  nearly  east  and  west 
around  the  globe. 

In  the  Arctic  climate,  vegetation  must  make  rapid 
growth  in  the  short,  cool  summer.  In  the  highest 
latitudes  the  summer  temperatures  are  not  high 
enough  to  melt  snow  on  a  level.  Exposure  is  there- 
fore of  the  greatest  importance.  Arctic  plants  grow 
and  blossom  with  great  rapidity  and  luxuriance  where 
the  exposure  is  favourable,  and  where  the  water  from 
the  melting  snow  can  run  off.  The  soil  then  dries 
quickly,  and  can  be  effectively  warmed.  On  the 
other  hand,  when  the  water  stands,  it  may  freeze  again 
and  again,  and  the  soil  underneath  has  no  oppor- 
tunity to  warm.  Of  Novaya  Zemlya  Baer  has  re- 
ported that  the  level  surfaces  are  polar  deserts,  while 
the  slopes  at  the  foot  of  the  mountains,  unless  covered 
with  boulders,  are  like  gardens  in  summer.  Protec- 
tion against  cold  winds  is  another  important  factor  in 
the  growth  of  this  vegetation.  Over  great  stretches 
of  the  northern  plains  the  surface  only  is  thawed  out 
in  the  warmer  months,  and  swamps,  mosses,  and 
lichens  are  found  above  eternally  frozen  ground. 


154  CLIMATE 

Trees  often  grow  in  favourable  conditions  along 
streams  when  the  intervening  plains  are  typical 
tundras.  Direct  insolation  is  very  effective  in  high 
latitudes.  Where  the  exposure  is  favourable,  snow 
melts  in  the  sun  even  when  the  temperature  of  the  air 
in  the  shade  is  far  below  freezing.  It  has  been  re- 
ported that  at  Assistance  Bay  (lat.  74%°  N.),  in 
March,  when  the  air  temperature  was  about  —  25°, 
snow  near  stones  and  other  dark  objects  melted  in  the 
sun.  Even  the  mean  daily  temperature  of  the  snow 
surface  may  be  higher  than  the  air  temperature.  The 
injurious  effect  of  polar  climate  upon  vegetation, 
especially  upon  trees,  has  been  attributed  by  Kihl- 
man n  to  an  insufficient  water-supply  furnished  by 
the  roots  deep  in  the  cold  ground.  From  the  upper 
parts  of  the  tree,  exposed  to  sunshine  and  wind,  evap- 
oration proceeds  rapidly,  and  the  tree  dries  up, 
^Protective  devices  against  excessive  evaporation,  not 
unlike  those  of  desert  plants,  arefounST" 

Arctic  and  Antarctic  zones  differ  a  good  deal  in 
the  distribution  and  arrangement  of  land  and  water 
around  and  in  them.  The  southern  zone  is  sur- 
rounded by  a  wide  belt  of  open  sea;  the  northern,  by 
land  areas.  The  northern  is  therefore  much  affected 
by  the  conditions  of  adjacent  continental  masses. 
Nevertheless,  the  general  characteristics  are  appar- 
ently much  the  same  over  both,  so  far  as  is  now 
known,  the  Antarctic  differing  from  the  Arctic 
chiefly  in  having  colder  summers,  and  in  the  regularity 
of  its  pressure  and  winds.  The  cold  Antarctic  sum- 


CHARACTERISTICS   OF  ZONES—  POLAR       155 
iners^arejhe  chief  cause  of  the  poverty  of  the  Antairc- 


Both  zones  have  the  lowest  mean  annual 

-•  - 

temperatures    in   their    respective    hemispheres,    and 
hence  may  properly  be  called  the  cold  zones. 


FIG.  30.    JANUARY  NORTH  POLAR  ISOTHERMS 

Temperature.  At  the  solstices,  the  two  poles  re- 
ceive the  largest  amounts  of  insolation  which  any  part 
of  the  earth's  surface  ever  receives.  It  would  seem, 
therefore,  that  the  polar  temperatures  should  then  be 
the  highest  in  the  world,  but  as  a  matter  of  fact  they 


156 


CLIMATE 


are  nearly  or  quite  the  lowest.  Temperatures  do  not 
follow  insolation  in  this  case  because  much  of  the  lat- 
ter never  reaches  the  earth's  surface;  because  most  of 


FIG.  31.    JULY  NORTH  POLAR  ISOTHERMS 

the  energy  which  does  reach  the  surface  is  expended 
in  melting  the  snow  and  ice  of  the  polar  areas;  and 
also  because  the  water  areas  are  large,  and  the  dura- 
tion of  insolation  is  short.  Hence  the  mean  annual 
temperatures  in  the  vicinity  of  the  poles  must  be 
very  low. 


CHARACTERISTICS   OF  ZONES— POLAR       157 

A  set  of  monthly  isothermal  charts  of  the  north 
polar  area,  based  on  all  available  observations,  was 
prepared  by  Mohn  and  published  in  the  volume  on 
Meteorology  of  the  Nansen  Expedition.  These 
charts  give  the  most  authentic  information  now  at 
hand  regarding  Arctic  temperatures.  In  the  winter 
months  there  are  three  cold  poles,  in  Siberia,  in 
Greenland,  and  at  the  pole  itself.  In  January,  the 
mean  temperatures  at  these  three  cold  poles  are  — 49  °> 
— 40°,  and  — 40°  respectively. 

The  Siberian  cold  pole  becomes  a  maximum  of  tem- 
perature during  the  summer,  but  the  Greenland  and 
polar  minima  remain  throughout  the  year.  In  April 
the  lowest  isotherm,  —  22°,  is  in  Greenland,  and  the 
north  pole  is  then  within  the  area  enclosed  by  —  18.4°. 
In  July  the  temperature  distribution  shows  consider- 
able uniformity;  the  gradients  are  relatively  weak. 

A  large  area  in  the  interior  of  Greenland,  and  one 
of  about  equal  extent  around  the  pole,  are  within  the 
isotherm  of  32°.  Hence  the  statement  frequently 
made,  that  no  places  in  the  northern  hemisphere  have 
mean  temperatures  below  freezing  in  July,  is  not  cor- 
rect. In  October  the  interior  of  Greenland  is  en- 
closed by  —  13°,  and  at  the  pole  we  find  —  11.2°.  For 
the  year~a  large  area  around  the  pole  is  enclosed  by 
the  isotherm  of  --4°,  with  an  isotherm  of  the  same 
value  in  the  interior  of  Greenland,  but  a  local  area 
of  —  7.6°  is  noted  in  Greenland,  and  one  of  --  11.2°  is 
centred  at  lat.  85°  N.  and  long.  170°  E.  It  will  be 
seen  that  the  temperatures  are  relatively  lower  to- 


158 


CLIMATE 


wards  the  eastern  sides  of  the  great  continents.  The 
ordinary  mean  annual  isothermal  chart  shows,  within 
the  Arctic  circle,  temperatures  of  40°  off  the  Nor- 
wegian coast  and  —  5°  beyond  lat.  75°  N.,  north  of 


FIG.  32.     MEAN  ANNUAL  NORTH  POLAR  ISOTHERMS 

Asia  and  North  America.  The  January  chart  shows 
30°  off  the  Norwegian  coast,  and  --60°  at  Verkho- 
yansk, in  Siberia.  The  July  chart  shows  60°  over  the 
continents,  to  40°  in  extreme  north-eastern  Asia. 


CHARACTERISTICS   OF  ZONES— POLAR       159 

The  north  polar  chart  of  annual  range  of  tempera- 
ture shows  a  maximum  range  of  about  120°  in  Siberia; 
of  80°  in  North  America;  of  75.6°  at  the  north  pole, 
and  of  72°  in  Greenland.  The  north  pole  obviously 
has  a  continental  climate.  The  minimum  ranges  are 
on  the  Atlantic  and  Pacific  oceans.  The  mean  an- 
nual isanomalies  show  that  the  line  of  zero  anomaly 
passes  through  the  pole  (as  it  must  do).  The  in- 
terior of  Greenland  has  a  negative  anomaly  in  all 
months.  The  Norwegian  sea  area  is  45°  too  warm  in 
January  and  February.  Siberia  has  +10.8°  in  sum- 
mer, and  —45°  in  January.  Between  Bering  Strait 
and  the  pole  there  is  a  negative  anomaly  in  all  months. 
The  influence  of  the  Gulf  Stream  drift  is  clearly  seen 
on  this  chart,  as  it  is  also  on  that  of  mean  annual 
ranges. 

The  mean  temperatures  of  the  higher  northern 
latitudes  in  January,  July,  and  for  the  year  have  been 
determined  by  Mohn  with  the  following  result: 

MEAN  TEMPERATURES   OF  THE    HIGHER  NORTHERN    LATITUDES. 

60°  65°           70°  75°  80°  85° 

Jan.                          +3.0°  -9.4°  -15.3°  -20.2°  -26.0°  -36.6° 

July                           57.4  54.3          45.1  38.1  35.6  32.5 

Year                          30.0  21.6          12.7  5.5  -0.6  -6.2 

For  the  north  pole  itself,  Mohn  gives  the  follow^ 
ing  results,  obtained  by  graphic  methods: 

MEAN   TEMPERATURES   OF   THE   NORTH    POLE. 

Jan.               Feb.          Mar.         Apr.  May  June       July 

-41.8°          -41.8°     -31.0°     -18.4°  8.6°  28.4°      30.2° 

Aug.         Sept.        Oct.          Nov.  Dec.  Year 

26.6°          8.6°        -11.2°     -27.4°  -36.4°  -8.9° 


160  CLIMATE 

It  appears  that  the  region  about  the  north  pole  is 
the  coldest  place  in  the  northern  hemisphere  for  the 
mean  of  the  year,  and  that  the  interior  ice  desert  of 
Greenland,  together  with  the  inner  polar  area,  are  to- 
gether the  coldest  parts  of  the  northern  hemisphere  in 
July.  In  January,  however,  Verkhoyansk,  in  north- 
eastern Siberia,  just  within  the  Arctic  circle,  has  a 
mean  temperature  of  about  —  60°,  while  the  inner 
polar  area  and  the  northern  interior  of  Greenland 
have  only  -  40°.  Future  exploration  in  the  im- 
mediate vicinity  of  the  north  pole  may  show 
a  lower  January  mean  temperature  there  than  at 
present  appears.  Such  exploration  will,  moreover, 
certainly  necessitate  readjustment  of  the  isothermal 
lines  as  now  drawn  for  this  polar  area.  It  may  be 
noted  that  the  isotherm  of  32°  in  January  crosses  the 
Arctic  circle  in  the  north-eastern  Atlantic.  Else- 
where it  is  south  of  this  line.  By  December  all  land 
within  the  Arctic  circle  is  below  the  freezing  point. 
Thus  far  no  minima  as  low  as  those  of  north-eastern 
Siberia  have  been  recorded  in  the  Arctic,  and  the 
Arctic  maxima  are  much  lower  than  those  of  Siberia. 
During  the  last  Peary  expedition,  the  winter  of 
1905-06  was  distinguished  by  "  comparatively  high  " 
temperatures. 

Until  about  twenty  years  ago,  the  available  obser- 
vations of  temperature  in  the  Antarctic  had  been  taken 
almost  altogether  in  the  summer  months.  Now  we 
know  a  good  deal  about  the  winter  temperatures 
around  the  margins  of  the  southern  circumpolar  area 


CHARACTERISTICS  OF  ZONES— POLAR        161 

as  well.  The  mean  temperatures  of  the  higher  lati- 
tudes of  the  southern  hemisphere  have  been  worked 
out  by  Meinardus,  with  the  following  results: 

MEAN   TEMPERATURES   OF   HIGH   SOUTHERN   LATITUDES 

S.  Lat.                                    60°  70°  80°  90° 

January  37.0°  29.7°  24.3°  21.2° 

July  12.9°  -7.6°  -19.7°  -27.9° 

Year  25.7°  9.0°  -5.1°  -13.  ° 

It  is  interesting  to  compare  these  temperatures 
with  those  given  on  page  159  for  the  corresponding 
latitudes  of  the  northern  hemisphere.  The  southern 
hemisphere  is  obviously  colder  than  the  northern  in 
these  higher  latitudes.  The  climate  of  the  south 
polar  zone  is  thus  distinctly  continental  in  char- 
acter, and  has  the  additional  unique  feature  of  a 
remarkably  cool  summer,  decidedly  cooler  than 
the  summer  of  the  Arctic  polar  area.  Important 
factors  in  lowering  the  Antarctic  temperatures  are 
the  Antarctic  continent,  with  its  great  permanent 
cover  of  snow  and  ice,  and  the  surrounding  cold 
oceans,  greatly  chilled  by  the  icebergs  and  floating 
ice-masses  which  have  broken  off  from  the  margins 
of  the  south  polar  land  mass.  In  the  north  polar 
area,  on4:he  other  hand,  warm  ocean  currents,  flowing 
northward,  keep  much  of  the  water  at  a  relatively  high 
temperature.  There  is  no  great  permanently  covered 
ice-mass,  with  the  exception  of  Greenland.  And  warm 
winds  from  more  southerly  latitudes  are  able  to  carry 
their  warmth  far  into  the  north  polar  zone. 


162  CLIMATE 

The  January  isotherm  of  32°  roughly  coincides 
with  the  Antarctic  circle,  or,  speaking  in  a  general 
way,  the  mean  temperature  of  the  warmest  month  is 
below  freezing  everywhere  inside  the  Antarctic  circle. 
At  Framheim  (lat.  78°  S.)  the  mean  tempera- 
ture of  the  warmest  month  was  20°. 8.  Within 
the  Arctic  circle,  on  the  other  hand,  mean  tempera- 
tures above  freezing  are  found,  except,  perhaps,  in 
the  interior  of  Greenland  and  around  the  north 
pole.  R.  C.  Mossman  has  contrasted  the  summer 
temperatures  of  the  northern  and  southern  polar 
areas  between  longs.  10°  E.  and  50°  W.  in  the  follow- 
ing striking  way.  In  the  southern  hemisphere, 
the  isotherm  of  35°  F.  nowhere  extends  beyond  lat. 
58°  S.;  in  the  northern,  it  reaches  as  far  as  lat.  81°  N., 
in  Spitzbergen.  At  long.  10°  E.  the  summer  isotherm 
of  34°  F.  is  only  about  550  miles  from  the  north  pole; 
on  the  same  meridian  in  the  southern  hemisphere 
the  distance  is  2300  miles.  The  low  mean  and  mini- 
mum temperatures  of  the  south  polar  summer  are 
responsible  for  much  of  the  difficulty  and  danger  of 
Antarctic  exploration.  They  prevent  much  melting 
of  snow  and  ice,  and  are  monotonous  and  depressing. 

The  temperatures  at  the  south  pole  itself  furnish 
an  interesting  subject  for  speculation.  Meinardus 
has  determined  them  to  be  —  13°  for  the  mean  annual; 
21.2°  for  January  and  -£7.9°  for  July.  The  cor- 
responding figures  for  the  north  pole  (Mohn)  are 
-  8.9°;  -  41.8°  and  30.2°.  On  the  basis  of  these  figures, 
the  south  pole  averages  9°  cooler  in  midsummer; 


CHARACTERISTICS  OF  ZONES— POLAR        163 

13.9°  warmer  in  midwinter,  and  4.1°  cooler  for  the 
whole  year,  than  the  north  pole.  It  is  not  yet  clear 
exactly  where  the  real  "cold  pole"  of  the  Antarctic 
is.  It  is  probably  not  at  the  south  pole  itself. 

The  mean  annual  temperatures  at  regular  stations 
in  the  Antarctic  have  as  a  whole  averaged  some- 
where between  about  25°  and  zero.  At  Framheini 
(lat.  78°  S.)  the  mean  annual  was  —  13.4°  (Hann), 
the  lowest  hitherto  recorded  anywhere  in  the  world. 
The  maxima  at  regular  stations  approach  50°  and 
the  minima  have  generally  been  in  the  vicinity  of 

—  40°   to  45°.     Lower  readings   have    been    made 
at  some  stations,  and  on  sledge  journeys  they  have 
been  as  low  as    -  60°,  —  70°,  and  nearly  to  --  75° 
(Amundsen).      Even    in    midsummer,    minima    of 

—  50°,  and  lower,  have  been  observed.     During  his 
sojourn  at  the  south  pole,  Amundsen  found  a  mean 
temperature  of  between  8  and  9°  F. 

The  annual  march  of  temperature  in  the  north 
polar  zone  is  peculiar  in  having  a  much-retarded 
minimum,  in  February  or  even  in  March — the  result 
of  the  long,  cold  winter.  The  temperature  rises 
rapidly  towards  summer,  and  reaches  a  maximum  in 
July.  Autumn  is  warmer  than  spring.  Winter 
comes  on  gradually,  the  summer  slowly  "falling 
asleep."  The  north  polar  type  of  annual  march  of 
temperature  is  illustrated  in  the  accompanying  curves 
(see  Fig.  33).  In  the  Antarctic  area,  the  mean 
temperatures  of  the  winter  months  (April  to  Septem- 
ber) are  surprisingly  uniform.  The  annual  tempera- 


F.  M.A..M.  J.  J.  A.  S.  Q.N.  0.  J. 


JL  F.  M.  A.  M.  J.  J.  A    S.  0  N.  D.  J. 


FIG.  33.  ANNUAL  MARCH  OF 
TEMPERATURE  :  POLAR  TYPE 

N.  Z.,  Novaya  Zemlya.  F.  J., 
Franz  Joseph's  Land.  G.  L. 
Grinnell  Land. 


164 


CHARACTERISTICS  OF  ZONES— POLAR        165 

ture  curve  is  flattened.  The  coldest  month  is  not 
nearly  as  emphatically  so  as  is  the  case  in  the  Arctic. 
Spring  is  apt  to  be  warmer  than  autumn.  The 
continents  do  not  penetrate  far  enough  into  the 
Arctic  zone  to  develop  a  pure  continental  climate 
in  the  highest  latitudes.  Verkhoyansk,  in  lat.  67°  6' 
N.,  almost  on  the  Arctic  circle,  furnishes  an  excellent 
example  of  an  exaggerated  continental  type  for  the 
margin  of  the  zone,  with  an  annual  range  of  120°. 
One-third  as  large  a  range  is  found  on  Novaya 
Zemlya.  The  diurnal  period  of  temperature  is  noted 
during  the  time  when  the  sun  is  visible,  but  is  hardly, 
or  not  at  all,  perceptible  during  the  dark  season. 
During  the  latter,  according  to  the  Fram  observa- 
tions, the  day  hours  are  usually  colder  than  the  night 
hours.  This  appears  to  be  an  effect  of  winds,  for 
colder,  northerly  winds  prevailed  during  the  hours  of 
daytime,  and  milder,  southerly  winds  by  night.  Polar 
climate  as  a  whole  has  large  annual  and  small 
diurnal  ranges,  but  sudden  changes  of  wind  may 
cause  marked  irregular  temperature  changes  within 
twenty-four  hours,  especially  in  winter.  The  small 
ranges  are  associated  with  greater  cloudiness,  and 
vice  versa.  The  mean  diurnal  variability  is  very 
small  in  summer,  and  reaches  its  maximum  in  win- 
ter, about  7°  in  February,  according  to  Mohn. 

Pressure  and  Winds.  Owing  to  the  more  sym- 
metrical distribution  of  land  and  water  in  the  south- 
ern than  in  the  northern  polar  area,  the  pressures  and 
winds  have  a  simpler  arrangement  in  the  former,  and 


166  CLIMATE 

may  be  first  considered.  Recent  Antarctic  explora- 
tion has  considerably  modified  some  of  the  views 
which  have  been  held  regarding  the  general  winds  of 
the  south  polar  area,  and  their  controlling  pressures. 
The  rapid  southward  decrease  of  pressure,  which 
is  so  marked  a  feature  of  the  higher  latitudes  of  the 
southern  hemisphere  on  the  isobaric  charts  of  the 
world,  does  not  continue  all  the  way  to  the  south 
pole.  Nor  do  the  prevailing  westerly  winds,  consti- 
tuting the  " circuinpolar  whirl,"  which  are  so  well 
developed  over  the  southern  portions  of  the  southern 
hemisphere  oceans,  blow  all  the  way  home  to  the 
south  pole.  The  steep  poleward  pressure  gradients  of 
these  southern  oceans  end  in  a  trough  of  low  pressure, 
girdling  the  earth  between  lats.  60°  and  70°  S. 
From  here,  the  pressure  increases  again  towards  the 
south  pole,  where  a  permanent  inner  polar  anti- 
cyclonic  area  is  found.  This  low  pressure  trough  is  an 
important  wind  divide.  Strong,  damp,  cloudy,  and 
snow-bearing  easterly  winds  have  been  reported 
from  stations  along  the  coasts  of  the  Antarctic 
continent.  These,  according  to  Meinardus,  are  cy- 
clonic winds  and  blow  from  lower  latitudes  into  the 
cyclonic  depressions  whose  paths  are  along  the  sub- 
Antarctic  low-pressure  trough.  The  relatively  high 
temperature  and  humidity  of  these  winds  are  thus 
explained  by  their  coming  from  warmer  latitudes, 
and  from  the  ocean.  They  are  not  dry,  as  they 
should  be  if  they  were  an  anticyclonic  outflow 
immediately  from  a  south  polar  barometric  maximum 


CHARACTERISTICS  OF  ZONES— POLAR        167 

over  the  interior  of  the  Antarctic  continent.  The 
limits  between  the  "prevailing  westerlies"  of  the 
southern  hemisphere  and  the  easterly  winds  flowing 
out  from  the  pole  vary  with  the  longitude  and  with 
the  season.  The  change  in  passing  from  one  wind 
regime  to  the  other  has  been  reported  upon  by 
several  Antarctic  observers.  The  prevalence  of  out- 
flowing winds  from  the  inner  south  polar  area  is 
evidenced  by  the  direction  of  the  ice  ridges  on  the 
polar  plateau. 

Meinardus  has  shown  that  the  Antarctic  anti- 
cyclone is  shallow,  and  probably  does  not  extend 
upward  even  to  the  height  of  the  land  itself.  Above 
about  6500  feet  (2000  metres),  over  this  anticyclone, 
with  its  outflowing  surface  winds,  there  is  a  polar 
cyclone,  with  an  inflowing  system  of  air  currents 
from  north  and  west,  i.  e.9  a  westerly  circumpolar 
whirl.  Observations  of  the  smoke-drift  from  Mt. 
Erebus,  and  of  the  upper  clouds,  confirm  this  view. 
These  upper  currents,  coming  from  the  vast  ocean 
area  surrounding  the  Antarctic  continent,  bring 
in  an  abundance  of  moisture  which  feeds  the  con- 
tinental ice-cap,  supplying  the  loss  due  to  the 
formation  of  icebergs,  and  to  evaporation.  The 
effect  of  the  Antarctic  anticyclone  is  thus  limited 
to  the  inner  and  lower  portions  of  the  Antarctic 
continent.  The  upper  portions  are  in  a  zone  of 
lower  pressure  and  of  westerly  winds.  Within  the 
area  occupied  by  the  anticyclone  the  winds,  ac- 
cording to  Meinardus,  are  prevailingly  easterly 


168  CLIMATE 

with  southerly  components.  Were  there  no  ele- 
vated land  masses  around  the  south  pole,  winds 
blowing  out  from  the  pole,  and  from  the  east, 
would  probably  prevail  throughout  the  high  pres- 
sure area.  Under  certain  conditions  the  winds 
from  the  Antarctic  continent  may  develop  high 
velocity  and  take  on  typical  foehn  characteristics, 
raising  the  temperature  to  an  unusually  high  degree. 
These  foehn  winds  have  been  a  conspicuous 
feature  at  several  Antarctic  stations,  especially  in 
winter,  when  the  high  temperatures  are  most  notice- 
able. They  are  also  known  on  both  coasts  of  Green- 
land, when  a  passing  cyclonic  depression  draws  the 
air  down  from  the  icy  interior.  These  Greenland 
foehn  winds  are  important  climatic  elements,  for 
they  blow  down  warm  and  dry,  raising  the  tempera- 
ture even  30°  or  40°  above  the  winter  mean,  and 
melting  the  snow. 

In  the  Arctic  area  the  wind  systems  are  less  clearly 
defined,  and  the  pressure  distribution  is  much  less 
regular  on  account  of  the  irregular  distribution  of 
land  and  water.  The  mean  pressure  as  a  whole 
increases  from  lat.  60°  N.  toward  the  north  pole. 
North-easterly,  i.  e.9  outflowing,  surface  winds  occur 
in  the  vicinity  of  the  pole  itself.  The  isobaric  charts 
published  in  the  report  of  the  Nansen  Expedition 
show  that  the  North  Atlantic  low  pressure  area  is 
more  or  less  well  developed  in  all  months.  In 
winter,  it  greatly  extends  its  limits  east  into  the 
inner  Arctic  Ocean,  to  the  north  of  Russia  and 


CHARACTERISTICS  OF  ZONES— POLAR        169 

Siberia.  Between  May  and  August  it  is  much  less 
well  developed.  The  Pacific  minimum  of  pressure 
is  found  south  of  Bering  Strait  and  in  Alaska.  Be- 
tween these  two  regions  of  lower  pressure,  the  divide 
extends  from  North  America  to  eastern  Siberia. 
This  divide  has  been  called  by  Supan  the  "Arktische 
Windscheide"  High  pressures  are  found  in  North 
America  and  in  Siberia  from  September  to  March, 
the  maxima  being  in  Asia.  The  belt  of  somewhat 
lower  pressure  connecting  these  two  maxima  is  situ- 
ated between  Bering  Strait  and  the  north  pole.  In 
July  and  August  the  maximum  pressure  is  between 
Greenland  and  somewhat  east  of  Spitzbergen.  The 
pressure  gradients  are  steepest  in  winter.  At  the 
pole  itself,  pressure  seems  to  be  highest  (about  30.079 
ins.)  in  April,  and  lowest  (29.882  ins.)  from  June  to 
September.  The  annual  range  is  therefore  only 
about  0.20  in. 

The  prevailing  westerlies,  which  in  the  high  south- 
ern latitudes  are  so  symmetrically  developed,  are  in- 
terfered with  to  such  an  extent  by  the  varying 
pressure  controls  over  the  northern  continents  and 
oceans,  in  summer  and  winter,  that  they  are  often 
hardly  recognisable  on  the  wind  maps.  The  isobaric 
and  wind  charts  prepared  by  Buchan  show  that  on 
the  whole  the  winds  blow  out  from  the  inner  polar 
basin,  especially  in  winter  and  spring.  During  his 
last  expedition,  in  the  winter  of  1905-06,  Peary 
reports  "  every  few  days  we  had  violent  winds  from 
the  south — sometimes  in  the  shape  of  squalls  of  a  few 


170  CLIMATE 

hours'  duration,  sometimes  continuing  as  furious 
gales  for  two  or  three  days."  During  a  westerly 
gale  of  six  days'  duration  (lat.  85°  12'  N.)  Peary  and 
members  of  his  party  drifted  some  seventy  miles  to 
the  eastward  on  the  ice. 

In  the  European  and  North  American  polar  areas 
the  annual  march  of  pressure  gives  a  spring  maxi- 
mum, in  April  and  May,  and  a  minimum  in  January 
or  February.  The  daily  fluctuations  in  pressure  in 
these  circumpolar  latitudes  are  about  twice  as  large 
in  winter  as  in  summer. 

Rain  and  Snow.  Rainfall  on  the  whole  decreases 
steadily  from  equator  to  poles.  The  amount  of  pre- 
cipitation must  of  necessity  be  comparatively  slight 
in  the  polar  zones  (15-10  ins.,  and  less),  chiefly  be- 
cause of  the  small  capacity  of  the  air  for  water  va- 
pour at  the  low  temperatures  there  prevailing ;  partly 
also  because  of  the  decrease,  or  absence,  of  local  con- 
vectlonal  storms  and  thunder-showers.1  Even  cy- 
clonic storms  cannot  yield  much  precipitation.  The 
polar  zones,  therefore,  have  a  permanent  deficiency 
of  precipitation.  Their  deserts  of  snow  and  ice  are 
climatic  deserts  in  more  senses  than  one.  These  ex- 
tended snow  and  ice  fields  naturally  tend  to  give  an 
exaggerated  idea  of  the  actual  amount  of  precipita- 
tion. It  must  be  remembered,  however,  that  evap- 
oration is  slow  at  low  temperatures,  and  melting  is 
not  excessive.  Hence  the  polar  store  of  fallen  snow 

1  Locally,  under  exceptional  conditions,  as  in  the  case  of  the  western 
coast  of  Norway,  the  rainfall  is  a  good  deal  heavier. 


CHARACTERISTICS  OF  ZONES— POLAR        171 

is  well  preserved;  interior  snow  fields,  ice  sheets,  and 
glaciers  are  produced.  Nansen  is  of  the  opinion  that 
the  amount  of  condensed  vapour,  much  of  it  being  in 
the  form  of  "  frozen  fog  "  (hoar  frost)  and  not  readily 
measurable,  exceeds  evaporation  in  the  polar  districts. 
The  commonest  form  of  precipitation  is  naturally 
snow,  the  summer  limit  of  which,  in  the  northern 
hemisphere,  is  near  the  Arctic  circle,  with  the  excep- 
tion of  Norway.  In  lat.  70°  N.,  at  Boothia  Felix, 
40  per  cent,  of  the  precipitation  from  June  to  August 
comes  in  the  form  of  snow.  So  far  as  exploration 
has  yet  gone  into  north  polar  latitudes,  rain  seems  to 
fall  in  summer.  It  is  doubtful  whether  there  are 
places  near  sea-level  where  all  the  precipitation  is 
snow.  It  is  also  uncertain  whether  any  mountains 
reach  a  height  where  nothing  but  snow  falls.  Von 
Drygalski  believes  that  the  inland  ice-cap  of  Green- 
land, over  £600  feet  above  sea-level,  meets  these 
conditions.  The  interior  of  the  Antarctic  continent 
probably  never  has  rain.  The  snow  of  the  polar 
regions  is  characteristically  fine  and  dry.  Schwa tka 
has  pointed  out  that  the  snow  huts  of  the  Eskimos 
could  not  be  built  with  the  kind  of  snow  that  falls 
in  the  United  States.  At  low  polar  temperatures 
flakes  of  snow  are  not  found,  but  precipitation  is  in 
the  form  of  ice  spicules.  The  finest  glittering  ice 
needles  ("diamond  dust")  often  fill  the  air,  even 
on  clear  days  and  in  calm  weather,  and,  gradually 
descending  to  the  surface,  slowly  add  to  the 
depth  of  snow  on  the  ground.  Dry  snow  is  also 


172  CLIMATE 

blown  up  from  the  snow-fields  on  windy  days,  inter- 
fering with  the  transparency  of  the  air.  Snowfalls 
at  temperatures  of  -  40°,  and  even  below,  have 
been  reported  from  eastern  Siberian  and  Arctic 
stations.  It  is  probable  that  under  these  conditions 
the  air  is  warmer  aloft. 

Humidity,  Cloudiness,  and  Fog.  The  absolute 
humidity  must  be  low  in  polar  latitudes,  especially 
in  winter,  on  account  of  the  low  temperatures.  Rela- 
tive humidity  varies  greatly,  and  very  low  readings 
have  often  been  recorded.  Cloudiness  seems  to  de- 
crease somewhat  towards  the  inner  polar  areas,  after 
passing  the  belt  of  much  cloudiness  in  the  higher 
latitudes  of  the  temperate  zones  (see  table,  p.  116). 
In  polar  climates,  the  summer  generally  has  the 
maximum  cloudiness;  the  winter  is  clearer.  The  data 
and  curve  given  below  illustrate  these  conditions 
(see  Fig.  34).  In  the  Antarctic  the  stations  at  the 
margins  of  the  polar  anticyclone  have  the  clearest 
skies.  The  summer  maximum  is  largely  due  to 
fogs,  which  are  produced  where  relatively  warm, 
damp  air  is  chilled  by  coming  in  contact  with  colder 
air  or  with  ice.  Open  water  in  the  midst  of  an  ice- 
covered  sea  is  often  detected  at  a  distance  by  means 
of  the  "steam  fog"  which  rises  from  it.  The  amount 
of  cloudiness  naturally  varies  considerably  with  the 
location  of  the  station,  and  with  the  prevailing  winds, 
as  is  the  case  in  warmer  latitudes.  Thus  the  coasts 
and  islands  bathed  by  the  warm  waters  of  the  Gulf 
Stream  drift  usually  have  a  higher  cloudiness  in 


CHARACTERISTICS  OF  ZONES— POLAR        173 

winter  than  in  summer.     The  place  of  fog  is  in  winter 
taken  by  the  fine  snow  crystals,  which  often  darken 

ANNUAL  MARCH   OF   CLOUDINESS   IN   POLAR   LATITUDES. 

MARINE  TYPE.     (Seven  stations.     Lat.  70°  N.) 

Jan.  Feb.  Mar.  Apr.    May  June  July  Aug.  Sept.  Oct.  Nov.  Dec.  Year 
7.1  6.9       6.4     7.0     7.7      8.3     8.5     8.2      8.0     8.0    6.8     6.6      7.5 


j.     F.     M.    A.    M.    J.     J.     A.     S.    0.    N.     0.     J. 


6 


4 


FIG.  34.    ANNUAL  MARCH  OF  CLOUDINESS  IN  THE  NORTH  POLAR 
ZONE  :  MARINE  TYPE 

the  air  like  fog  when  strong  winds  raise  the  dry 
snow  from  the  surfaces  on  which  it  is  lying. 

Our  knowledge  concerning  cloud  forms  and  move- 
ments in  the  polar  zones  has  increased  rapidly  during 
recent  .years,  especially  for  the  Antarctic.  The 
records  of  the  Nansen  expedition  show  a  greater 
cloudiness  by  day,  and  with  stronger  winds.  Cumulus 
forms  are  rare,  even  in  summer,  and  it  is  doubtful 
whether  this  cloud  occurs  at  all  in  its  most  typical 
development.  Clearly  defined  cloud  forms  have 


174  CLIMATE 

been  reported  by  some  observers  to  be  very  rare  in- 
deed in  the  Arctic,  especially  in  the  winter  sky.  On 
the  other  hand,  Lieutenant  Royds,  of  the  Discovery, 
reports  that  he  never  saw  such  striking  and  beautiful 
examples  of  every  kind  of  cloud  as  within  the  Antarc- 
tic circle.  At  Griffith  Island,  in  the  north  polar  zone, 
two  months  passed  without  clouds.  And  "day  after 
day,  with  glorious  clear  skies  and  continuous  sun- 
shine" is  reported  by  the  Discovery  in  the  Antarctic. 
Stratus  is  probably  the  commonest  cloud  of  high 
latitudes,  often  covering  the  sky  for  days  without  a 
break.  In  place  of  well-developed  cloud  forms, 
the  air  is  filled  with  fog  in  summer,  which  often  grows 
into  poorly  defined  stratus  clouds.  Cirrus  forms 
follow  stratus  in  frequency.  Nansen's  results  give 
an  average  cloud  movement  from  W.  N.  W.  and  N. 
TV.  In  the  Antarctic,  the  upper  clouds  come  from 
westerly  directions.  The  Belgica  expedition  noted 
cirrus  from  the  east  in  summer  only.  At  the  South 
Orkneys,  cirrus  was  observed  at  altitudes  of  6000  to 
8000  feet. 

Cyclones  and  Weather.  The  prevailing  westerlies 
continue  up  into  the  margins  of  the  polar  zones. 
Many  of  their  cyclonic  storms — the  weather  controls 
of  temperate  latitudes — also  continue  on  to  the  polar 
zones,  giving  sudden  and  irregular  pressure  and 
weather  changes.  The  inner  polar  areas  seem  to 
be  beyond  the  reach  of  frequent  and  violent  cyclonic 
disturbance.  Calms  are  more  common;  the  weather 
is  quieter  and  fairer;  precipitation  is  less.  Most 


CHARACTERISTICS  OF  ZONES—POLAR        175 

of  the  observations  thus  far  obtained  from  both 
polar  zones  naturally  come  from  this  marginal  zone  of 
greater  cyclonic  activity,  violent  winds,  and  snowy, 
disagreeable,  inhospitable  weather,  and  therefore 
do  not  show  the  features  of  the  actual  polar  climate. 

A  very  thorough  study  of  cyclonic  movements  in 
the  highest  latitudes  was  made  in  connection  with  the 
Nansen  expedition  in  the  Fram.  During  the  three 
years  of  her  drift,  depressions  passed  on  all  sides  of 
her,  with  a  preponderance  on  the  west.  The  direc- 
tion of  progression  averaged  nearly  due  east,  and 
the  hourly  velocity  twenty-seven  to  thirty-four  miles, 
which  is  about  that  in  the  United  States.  The  rainy 
winds  were  usually  S.  and  S.E.,  while  N.E.  and  N.W. 
were  least  likely  to  bring  rain  or  snow.  For  the 
higher  latitudes,  most  of  the  cyclones  must  pass  by 
on  the  equatorial  side  of  the  observer,  giving  "  back- 
ing "  winds  in  the  northern  hemisphere.  The  main 
cyclonic  tracks  are  such  that  the  wind  characteristi- 
cally backs  in  Iceland,  and  still  more  so  in  Jan  Mayen 
and  on  the  eastern  coast  of  Greenland,  these  districts 
lying  on  the  north  and  west  of  the  path  of  progres- 
sion. Frightful  winter  storms  occasionally  occur 
along  the  east  coast  of  Greenland  and  off  Spitzber- 
gen.  During  the  drift  of  the  Fram  the  southerly 
winds,  were  the  warmest  in  winter  and  the  northerly 
the  coldest,  showing  that,  at  the  82d  parallel  of  lati- 
tude, the  Siberian  cold  pole  ceases  to  have  much 
influence. 

For  much  of  the  year  in  the  polar  zones  the  diurnal 


176  CLIMATE 

control  is  weak  or  absent.  The  successive  spells  of 
stormy  or  of  fine  weather  are  wholly  cyclonically 
controlled.  Extraordinary  records  of  storm  and 
gale  have  been  brought  back  from  the  far  south  and 
the  far  north.  The  Swedish  Antarctic  expedition, 
for  example,  under  Nordenskjold,  in  1902-03,  ex- 
perienced for  five  months,  beginning  in  May,  a  period 
of  storms  with  short  intermissions  never  exceeding 
three  days,  and  during  all  of  this  period  the  average 
wind  velocity  was  twenty-three  miles  an  hour,  and 
for  a  fortnight  it  averaged  forty-five  miles.  The 
Discovery  reported  a  gale  on  July  19,  1902,  which 
lasted  ten  hours  with  a  velocity  of  eighty-five  miles 
an  hour.  The  Mawson  expedition  brought  back 
from  the  coast  of  Wilkes  Land  a  record  of  an  average 
wind  velocity  throughout  the  year  of  nearly  fifty  miles 
an  hour.  Hourly  velocities  of  one  hundred  miles  were 
not  uncommon.  This  particular  locality  seems  at  pre- 
sent to  possess  the  unenviable  reputation  of  being  the 
windiest  region  in  the  world.  It  is  truly  the  "home 
of  the  blizzard."  Over  the  marginal  area  between  the 
Antarctic  continent  and  its  surrounding  oceans  is  a 
storm  belt  which,  for  frequency  and  intensity  of  its 
cyclones,  is  unequalled.  Gales,  and  snows,  and 
cold:  these  are  the  dominant  climatic  features. 

During  a  northern  polar  winter  the  average  thick- 
ness of  ice  formed  over  the  oceans,  where  no  storms 
or  strong  tides  interfere,  reaches  six  feet  and  more. 
Nansen  found  a  thickness  of  over  eight  feet  in  one 
year.  During  the  long  summer  days  the  temperature 


CHARACTERISTICS  OF  ZONES— POLAR        177 

rises  well  above  the  winter  mean,  and  under  favour- 
able conditions  certain  phenomena, such  as  the  diurnal 
variation  in  wind  velocity,  for  example,  give  evidence 
of  the  diurnal  control.  But  the  irregular  cyclonic 
weather  changes  continue,  in  a  modified  form. 
There  is  no  really  warm  season.  Snow  still  falls. 
The  summer  is  essentially  only  a  modified  winter. 
Its  clear  spells  are  relatively  warm,  and  winds  bring 
lower  temperatures.  In  spite  of  its  lack  of  high 
temperatures,  the  northern  polar  summer,  near  the 
margins  of  the  zone,  has  many  attractive  qualities 
in  its  clean,  pure,  crisp,  dry  air,  free  from  dust  and 
impurities;  its  strong  insolation;  its  slight  precipita- 
tion. The  prevalent  summer  fogs  are  a  serious 
disadvantage. 

Twilight  and  Optical  Phenomena.  The  monotony 
and  darkness  of  the  polar  night  are  decreased  a  good 
deal  by  the  long  twilight,  due  to  the  high  degree  of 
refraction  at  low  temperatures.  The  sun  actually 
appears  and  disappears  some  days  before  and  after 
the  times  which  are  geometrically  set.  Light  from 
moon  and  stars,  and  from  the  aurora,  also  relieves  the 
darkness.  Optical  phenomena  of  great  variety, 
beauty,  and  complexity  are  common.  Solar  and 
lunar  haloes  and  coronas,  and  mock  suns  and  moons 
are  often  seen.  Auroras  seem  to  be  less  common  and 
less  brilliant  in  the  Antarctic  than  in  the  Arctic. 
Sunset  and  sunrise  colours  within  the  polar  zones  are 
described  as  being  extraordinarily  brilliant  and 
impressive. 


CHAPTER  VII 

THE  HYGIENE  OF  THE  ZONES 

Introduction:  Some  General  Relations  of  Climate  and  Health — 
A  Complex  Subject — Climate,  Micro-organisms  and  Disease — 
Geographical  Distribution  of  Disease — Tropics:  General  Physi- 
ological Effects — Tropical  Death-rates — Hygiene  in  the 
Tropics — Tropical  Diseases — Malaria — Yellow  Fever — Dys- 
entery— Diarrhoeal  Disorders — Tropical  Abscess  of  the  Liver 
— Cholera — Plague — Sunstroke  and  Related  Conditions — 
Dengue — Beri-beri — Other  Minor  Diseases — General  Con- 
clusions: Tropics — Temperate  Zones:  General — Winter  and 
Summer  Diseases — Tuberculosis — Pneumonia — Diphtheria — 
Influenza — Bronchitis — Rheumatism — Measles  and  Scarlet 
Fever — Typhoid  Fever — Whooping  Cough — Cholera  Infantum 
—Hay  Fever— Polar  Zones:  General— Scurvy— Climate  and 
Health:  General  Conclusions. 

Introduction:  Some  General  Relations  of  Climate 
and  Health.  From  earliest  times  people  have  sought 
in  atmospheric  conditions  an  explanation  of  the  oc- 
currence of  disease,  and  have  often  found  in  statistics 
of  mortality  and  of  weather  a  more  or  less  striking 
parallelism.  Many  fairly  obvious  facts  naturally 
point  to  some  relation  of  cause  and  effect  in  this 
matter.  Some  diseases  are  found  principally  in 
the  warmer  climates ;  others  seem  to  prefer  the  colder. 

178 


TEE  HYGIENE  OF  THE  ZONE 'S  179 

Some  are  usually  more  active  in  the  warmer,  or  the 
drier,  months;  others  have  shown  the  contrary  rela- 
tion. High  altitudes  are  free  from  some  diseases 
which  prevail  near  sea-level,  and  have  certain  favour- 
able climatic  characteristics  long  recognised  in  the 
treatment  of  disease.  The  pure  air,  increased  res- 
piration, and  deeper  breathing  are  stimulating  and 
health-giving;  they  are  beneficial  in  many  affections 
of  the  lungs,  although  occasionally  over-stimulating 
in  nervous  and  cardiac  troubles.  In  the  case  of  other 
diseases,  again,  altitude  has  no  effect.  Dry  climates, 
especially  deserts,  whose  air  is  usually  exceptionally 
pure  and  aseptic,  are  generally  healthful,  and  are 
beneficial  in  many  cases  where  mountain  climates  are 
too  stimulating.  The  climates  within  forested  areas 
have  proved  especially  favourable  in  cases  of  phthisis. 
Ocean  air,  pure  and  dust-free,  with  its  saline  con- 
stituents and  equability  of  temperature,  is  beneficial 
to  most  persons  as  a  moderate  tonic  and  as  a  restora- 
tive in  many  illnesses.  Winds  are  important  agents 
in  promoting  health.  The  cool,  refreshing  sea-breeze 
of  the  tropics  brings  in  pure  air  from  the  sea,  and  is 
one  of  the  most  important  desiderata  in  hot  climates. 
Winds  are  active  ventilating  and  purifying  agents 
where  population  is  congested.  Fogs  and  clouds,  by 
cutting  off  sunlight,  weaken  one  of  the  best  agents  in 
promoting  health,  for  the  germicidal  action  of  sun- 
light has  been  proved  by  many  investigators.  Stern- 
berg  has  called  it  "  one  of  the  most  potent  and  one 
of  the  cheapest  agents  for  the  destruction  of  patho- 


180  CLIMATE 

genie  bacteria,"  and  says  "  its  use  for  this  purpose  is 
to  be  recommended  in  making  practical  hygienic 
recommendations."  In  London,  a  higher  death-rate 
after  a  long  fog  may,  however,  result  from  the  lower 
temperature  during  the  fog,  and  not  from  any  direct 
effect  of  the  fog  itself. 

A  Complex  Subject.  Facts  like  the  foregoing 
naturally  prejudice  one  in  favour  of  a  causal  connec- 
tion between  atmospheric  conditions  and  disease. 
Nevertheless,  such  studies  have  often  led  to  very  con- 
tradictory conclusions.  Diseases  usually  character- 
istic of  one  zone  are  known  to  spread  widely  over 
other  zones.  Diseases  which  usually  prefer  the 
warmer  months  sometimes  occur  in  the  coldest. 
Rules,  previously  determined  as  the  result  of  careful 
investigation,  often  break  down  in  a  most  perplex- 
ing way.  Some  of  the  difficulty  in  this  lack  of  agree- 
ment results  from  untrustworthy  statistics,  often 
collected  under  very  varying  conditions  and  really 
not  comparable.  Curves  are  smoothed  to  such  an  ex- 
tent that  they  can  be  made  to  show  anything.  Conclu- 
sions are  drawn  in  individual  cases  which  are  neither 
of  general  application,  nor  do  they  even  apply  locally 
on  any  other  occasion  than  the  special  one  in  question. 
Most  of  this  disagreement  comes  from  the  fact 
that  not  only  may  the  different  weather  elements 
themselves,  temperature,  moisture,  wind,  sunshine, 
and  so  on,  each  have  some  effect  in  the  produc- 
tion of  a  disease,  which  it  is  impossible  to  determine, 
but  so  many  other  factors  are  concerned  in  the  mat- 


THE  HYGIENE  OF  THE  ZONES  181 

ter  that  confusion  and  contradiction  in  the  conclusions 
reached  are  inevitable.  Sanitation,  food,  water,  habits, 
altitude,  character  and  moisture  of  the  soil,  race, 
traffic,  and  other  controls  serve  to  complicate  the 
problem  still  further.  In  most  studies  of  climate 
and  health  some,  or  even  many,  of  these  factors  have 
not  received  attention.  Hence  the  results  have 
usually  been  incomplete.  Local,  peculiar,  and  tem- 
porary conditions  may  play  a  large  part  in  the  pre- 
valence of  disease.  Overcrowding  under  unhygienic 
conditions,  especially  indoors  during  cold  weather, 
and  traffic  by  rail,  steam,  caravan,  or  on  foot,  are  often 
more  important  than  climate.  The  frequent  escape 
of  mountain,  of  desert,  and  of  polar  peoples  from  epi- 
demics is  to  be  attributed  in  most  cases  to  the  smaller 
chance  of  importing  disease  because  of  little  inter- 
course with  the  outside  world,  and  of  spreading  it, 
when  imported,  because  of  the  scattered  population. 
It  may  be  noted,  however,  that  the  crowding  indoors 
and  the  sparseness  of  population  in  these  two  cases 
are  more  or  less  directly  climatically  controlled. 

Climate,  Micro-organisms  and  Disease.  The 
cause  of  disease  is  now  no  longer  sought  directly 
in  meteorological  conditions,  but  in  the  effects,  more 
or  less  direct,  of  these  conditions  upon  the  micro- 
organisms which  are  the  specific  cause  of  the  disease. 
Atmospheric  conditions  may  help  or  may  retard  the 
development  of  the  micro-organism,  and  may 
strengthen  or  weaken  the  individual's  power  of 
resistance  against  the  attacks  of  the  germ,  as  well  as 


182  CLIMATE 

affect  his  susceptibility.  Thus  new  views  have  re- 
placed the  old.  Winds  used  to  be  regarded  as  the 
chief  agents  in  spreading  epidemics:  now  it  is  known 
that  disease  cannot  be  carried  far  by  winds,  for  the 
micro-organisms  do  not  long  maintain  their  power  in 
the  free  air  and  under  the  sun.  Rain  has  been  sup- 
posed directly  to  control  the  distribution  of  diseases: 
now  we  believe  that  precipitation  acts  only  indirectly, 
through  drinking  water,  or  through  its  control  of 
the  dust  in  the  air.  Dust  from  dry  soil  may 
contain  the  germs  of  infectious  diseases,  and  aggra- 
vates affections  of  the  respiratory  organs.  Harm- 
ful exhalations  are  no  longer  believed  to  be  given  off 
by  the  soil,  but  the  condition  of  the  soil  as  to  moisture 
and  temperature  may  affect  the  development  and 
diffusion  of  certain  micro-organisms.  Some  parallel- 
ism has  been  discovered  between  the  prevalence  of 
certain  diseases,  such  as  diarrhoea  and  typhoid  fever, 
and  soil  temperatures  or  the  ground-water  level. 

Geographical  Distribution  of  Disease.  The  scheme 
of  classifying  disease  geographically,  on  a  broad 
climatic  basis,  is  attractive,  but  not  very  satisfactory. 
For,  on  the  one  hand,  many  diseases  are  practically 
universal  in  extent,  showing  great  independence  of 
climate,  and  on  the  other,  the  history  of  many  dis- 
eases is  still  in  the  making.  In  the  distribution  of 
disease  too  many  factors  are  concerned  to  make  any 
simple  and  accurate  treatment  possible  as  yet.  In 
spite  of  this  complexity,  however,  certain  broad  gen- 
eral statements  may  be  made,  useful  in  enabling  the 


THE  HYGIENE  OF  THE  ZONES  183 

layman  properly  to  co-ordinate  his  ideas  on  the  sub- 
ject, and  fairly  accurate  within  reasonable  limits. 

Tropics:  General  Physiological  Effects.  The  uni- 
formly high  temperatures  of  the  tropics,  especially 
when  combined  with  high  humidity  and  the  character- 
istically small  diurnal  variability  of  temperature, 
have  certain  fairly  well  established  physiological 
effects.  Among  these  the  following  are  commonly 
noted:  increased  respiration;  decreased  pulse  action; 
profuse  perspiration;  lessened  activity  of  stomach 
and  intestines,  and  tendency  to  digestive  disorders;  a 
depression  of  bodily  and  mental  activity,  enervation, 
indifference,  disinclination  to  exertion, — in  fact,  a 
general,  ill-defined  condition  of  debility;  increased 
activity  of  the  liver;  surexcitation  of  the  kidneys.  In 
damp,  hot  air,  evaporation  from  lungs  is  slight;  the 
blood  becomes  more  diluted;  there  is  a  deficiency  in 
the  number  of  red  corpuscles  in  consequence  of  the 
diminished  proportion  of  oxygen  in  the  air.  There 
is  less  power  to  do  work;  greater  fatigue  from  work; 
lowered  vitality.  All  this  renders  the  body  less  able 
to  resist  disease.  An  anaemic  condition  in  the  moist 
tropics  is  widespread. 

Tropical  Death-rates.  As  compared  with  the 
death-rates  in  colder  latitudes,  tropical  death-rates 
average  high.  They  range  from  the  appalling  rate 
of  483  per  1000  among  European  troops  on  the  Gold 
Coast  in  1829-1836,  through  121  per  1000  for 
European  troops  in  Jamaica  in  1820-1836,  down  to 
so  low  a  rate  as  14.84  per  1000  for  British  troops  in 


184  CLIMATE 

India  in  1896.  These  death-rates,  however,  repre- 
sent such  very  diverse  conditions  of  season,  climate, 
race,  occupation,  soil,  mode  of  life,  food,  dwelling, 
etc.,  that  they  cannot  legitimately  be  compared  with 
one  another.  The  prevalence  of  some  special  dis- 
ease in  exceptionally  virulent  or  widespread  develop- 
ment will  raise  the  death-rate  of  any  year  far 
beyond  its  usual  figure.  Again,  the  presence  of  some 
insect  which  causes  loss  of  crops,  and  the  resulting 
lowered  vitality  of  the  people  in  consequence  of  in- 
sufficient food,  may  easily  swell  the  death-rate.  Nor 
can  these  tropical  death-rates  properly  be  compared 
with  the  death-rates  noted  under  different  conditions 
in  other  latitudes.  (A  recent  attempt  to  compare  the 
death-rate  among  American  troops  in  the  Philippines 
with  the  general  death-rate  in  certain  American  cities 
is  an  excellent  example  of  the  danger  of  comparing 
two  totally  different  things).  So  various  and  so 
complex  are  the  controlling  factors  that  critical  com- 
parative study  is  not  worth  while.  Tropical  death- 
rates  are  certainly  high,  but  this  fact  should  not  be 
attributed  solely  to  the  dangers  of  the  climate.  Bad 
sanitary  conditions  and  lack  of  medical  attendance 
account  for  many,  if  not  most,  of  the  high  tropical 
death-rates  among  the  natives ;  and  an  irrational  mode 
of  life  explains  many  deaths  among  persons  coming 
from  cooler  climates.  Tropical  death-rates  are  be- 
ing reduced  with  remarkable  rapidity  in  all  coun- 
tries which  are  wholly  or  partly  under  white  control, 
and  especially  among  European  troops  in  the 


THE  HYGIENE  OF  THE  ZONES  185 

tropics.  This  is  the  result  of  experience  with  tropical 
conditions,  and  of  the  increased  precautions  which 
are  now  taken  in  selecting  and  caring  for  the  men. 

Hygiene  in  the  Tropics.  Under  the  special  condi- 
tions of  tropical  climates,  the  resident  who  comes 
from  a  cooler  latitude  needs  to  take  special  precau- 
tions regarding  his  mode  of  life  and  personal  hy- 
giene. A  rational,  temperate  mode  of  life,  especially 
the  avoidance  of  alcoholic  excess;  regular  exercise; 
non-fat-producing  food;  clothing  suited  to  the  cli- 
mate, such  as  duck  or  linen  for  outside  garments  dur- 
ing the  day,  and  light  woollen  for  the  cool  of  the 
evening  and  night;  careful  attention  to  the  site  and 
construction  of  dwellings;  all  possible  sanitary  pre- 
cautions; keeping  cool  during  the  warmest  hours  and 
season  by  the  use  of  fans  or  punkahs,  by  frequent 
baths,  and  by  abstaining  from  hard  work;  protection 
against  mosquitoes  by  means  of  screens;  frequent 
change  of  climate  by  returning  to  cooler  latitudes,— 
all  these  are  important.  It  seems  like  a  contradic- 
tion, but  it  is  a  fact,  that  the  danger  of  taking  cold 
in  the  tropics  is  very  great,  and  must  be  carefully 
guarded  against.  General  Wolseley  is  reported  to 
have  said  of  the  tropics,  "  not  to  get  cold  is  to  avoid 
almost  certainly  all  the  causes  of  disease,"  and  a  re- 
cent writer  has  well  said  that  these  words  should  be 
inscribed  on  the  walls  of  all  barracks  in  the  tropics. 
The  situation  may  be  summed  up  in  the  rule:  "  Re- 
spect the  sun,  and  rain,  and  wind ;  clothe  with  a  view 
to  avoiding  chill,  and  live  temperately."  The  dan- 


186  CLIMATE 

ger  of  becoming  chilled  is  greatest  during  the  cooler 
hours  of  evening  and  night,  during  rains,  or  when 
cool  winds  blow.  The  skin  does  not  react  well  in  the 
tropics,  hence  chills  are  frequent  with  even  slight  tem- 
perature changes,  especially  when  there  is  wind.  As 
to  the  best  style  of  dwelling  for  the  tropics,  there  is 
no  absolute  agreement.  The  material  can  best  be 
determined  by  the  local  conditions  in  each  case. 
Wood,  stone,  and  thatch  are  employed  successfully. 
Of  whatever  construction,  houses  should  be  roomy 
and  airy,  and  protected  against  direct  sunshine  dur- 
ing the  hottest  hours  of  the  day. 

Tropical  Diseases.  In  addition  to  the  physiologi- 
cal effects  just  considered,  certain  diseases  are  so 
much  at  home  in  the  tropics  that  they  have  come  to 
be  known  as  tropical  diseases.  This  designation, 
however,  as  Sir  Patrick  Manson  uses  it  in  the  title  of 
his  famous  work,  does  not  mean  diseases  confined 
to  the  tropics,  but  is  employed  in  a  meteorological 
sense  for  diseases  associated  with,  but  not  solely  or 
even  directly  due  to,  high  temperatures.  Tropical 
climatic  conditions,  per  se,  probably  do  not  injuri- 
ously affect  the  natives  of  the  tropics  any  more  than 
do  the  conditions  of  extra-tropical  climates  affect 
those  who  live  in  them. 

Sir  Patrick  Manson  has  made  the  fact  very  clear 
that  the  difference  between  the  diseases  of  tropical 
and  extra-tropical  latitudes  lies  in  the  specific  cause 
of  these  diseases.  For  the  development  of  certain 
disease  germs,  certain  temperatures  are  required. 


THE  HYGIENE  OF  THE  ZONES  187 

Sometimes  the  temperature  is  too  high;  sometimes 
too  low.  Again,  certain  media  are  necessary  in 
propagating  certain  diseases,  as  e.  g.,  a  third  organ- 
ism, other  than  the  disease  germ  itself,  and  man,  who 
has  the  disease.  The  third  organism  may  be  a  tropi- 
cal species,  as  in  the  case  of  the  tsetse  fly;  if  so,  the 
disease  is  a  tropical  disease.  The  opportunity  for 
contracting  the  disease  is  best,  or  exists  solely,  in  the 
tropics.  Again,  some  diseases  are  the  result  of 
toxins  generated  by  germs  living  in  an  external  med- 
ium. One  condition  of  development  of  these  germs 
may  be  a  certain  high  temperature.  Thus  the  dis- 
ease is  a  tropical  disease,  e.  g.,  beri-beri.  On  the 
other  hand,  when  everything  seems  favourable,  nat- 
ural enemies  of  the  germs  themselves,  or  of  the 
organism  which  subtends  the  germs,  may  destroy 
them.  Dr.  Manson's  conclusion,  which  is  the  result 
of  careful  study,  may  well  be  accepted  as  an  authori- 
tative statement.  "  The  more  we  learn  about  these 
diseases,  the  less  important  in  its  bearing  on  their 
geographic  distribution,  and  as  a  direct  pathogenic 
agency,  becomes  the  role  of  temperature  per  se,  and 
the  more  the  influence  of  the  tropical  fauna." 

Besides  the  more  or  less  direct  effects  of  exposure 
to  tropical  sun  and  heat,  such  as  sunstroke,  heat  ex- 
haustion, and  the  like,  there  are  malaria,  in  varied 
forms,  and  dysentery,  the  two  worst  enemies  of  white 
residents  in  the  tropics;  dengue;  ulcers;  yaws;  tropi- 
cal abscess  of  the  liver,  a  common  and  dreaded  dis- 
ease; diseases  like  yellow  fever,  cholera,  and  plague, 


188  CLIMATE 

which  are  more  or  less  limited  to  certain  localities,  and 
are  being  hemmed  in  more  and  more  by  modern  sani- 
tary measures;  many  other  infectious  diseases  which 
are  common  to  colder  as  well  as  warmer  latitudes ;  and 
beri-beri,  elephantiasis,  and  other  diseases  which  at- 
tack the  coloured  race  chiefly,  and  are  therefore  of  a 
medical  rather  than  of  a  practical  interest  to  white 
people.  The  fact  that  plague,  and  leprosy,  and  to 
some  extent  cholera  as  well,  are  practically  limited 
to  the  tropics,  is  the  result  of  modern  sanitary  precau- 
tions in  the  extra-tropics.  The  unsanitary  condi- 
tions among  tropical  peoples  favour  the  spread  of 
these  and  similar  diseases,  and  not  the  climate  per 
se.  Nevertheless  it  is  as  clear  as  day,  in  the  words  of 
Dr.  Manson,  that  these  very  unsanitary  conditions 
are  "  more  or  less  an  indirect  outcome  of  tropical  cli- 
mate." There  is  a  greater  variety  in  tropical  than 
in  extra-tropical  diseases,  but  then  many  diseases 
common  in  cooler  latitudes  prevail  also  near  the 
equator,  and  many  diseases  prevail  near  the  equator 
which  have  practically  been  banished  from  higher 
latitudes.  Tropical  climate  is  not  the  sole,  or  even 
in  many  cases  the  determining  factor.  Most 
tropical  diseases  attack  both  natives  and  whites; 
sometimes  the  former  suffer  most;  sometimes  the 
latter.  There  is  no  rigid  rule ;  but  the  racial  element 
is  often  very  potent. 

Malaria.  Malaria,  next  to  tuberculosis  one  of  the 
most  important  of  diseases,  was  formerly  considered 
a  poisonous,  gaseous  emanation  from  the  soil.  It  is 


THE  HYGIENE  OF  THE  ZONES  189 

now  known  to  be  a  germ  disease.  In  1880,  Laveran, 
a  French  army  surgeon  in  Algiers,  discovered  a  para- 
site in  the  blood  of  malarious  persons.  Manson  later 
suspected  mosquitoes  as  the  means  of  propagating 
the  malarial  parasite.  (Dr.  A.  F.  A.  King,  of 
Washington,  D.  C.,  had  advanced  a  similar  sugges- 
tion in  1841.)  Ross,  at  Manson's  suggestion  in 
1894,  followed  up  the  clue  in  India,  and  established 
the  fact.  His  work,  and  that  of  Grassi,  Koch,  and 
others,  has  shown  that  the  insect  here  concerned  is  a 
mosquito  of  the  single  genus  Anopheles,,  and  that 
malaria  is  due  mainly,  if  not  solely,  to  the  injection 
of  the  parasites  into  the  blood  of  human  beings  by 
the  bite  of  mosquitoes  previously  infected  by  stinging 
some  human  being  suffering  from  malaria. 

Malaria  is  very  widely  distributed,  from  the  polar 
circles  to  the  equator,  but  the  endemic  foci,  Manson 
points  out,  tend  to  become  more  numerous  towards 
the  equator.  There  is,  on  the  whole,  a  fairly  regular 
decrease  in  frequency  and  in  severity  from  equator 
poleward.  In  certain  parts  of  the  tropics,  as,  for  ex- 
ample, the  Gold  Coast,  the  mouths  of  the  Congo  and 
Zambesi,  New  Guinea,  etc.,  malaria  is  so  prevalent 
and  so  severe  that  the  question  of  residence  there  for 
the  white  race  has  been  practically  controlled  thereby. 
The-  disease  is  commonly  associated  with  swamps, 
and  moist  low-lying  districts,  while  uplands  and 
well-drained  areas  are  usually  less  affected.  This 
relation,  however,  seems  to  be  somewhat  less  appar- 
ent in  the  tropics  than  in  higher  latitudes.  Malaria 


190  CLIMATE 

is  perennial  in  the  tropics,  with  a  general  tendency  to 
a  maximum  in  the  warmer  or  rainy  season.  In  the 
temperate  zone  the  maximum  is  in  late  summer  or 
early  autumn. 

It  is  clear,  with  the  mosquito  theory  so  well  estab- 
lished that  Koch  can  say,  of  tropical  Africa,  "  where 
there  are  mosquitoes  there  is  malaria,  and  where  there 
are  no  mosquitoes  there  is  no  malaria,"  that  the  older 
views  regarding  the  relation  of  climate  and  soil  to 
malaria  must  have  undergone  some  change.  Never- 
theless, there  is  still  a  fairly  definite  relation  of  cause 
and  effect  in  this  matter.  For  the  development  of 
the  malarial  parasite  in  the  body  of  the  mosquito  a 
certain  degree  of  heat  is  necessary,  probably  a  mean 
temperature  of  at  least  60°  F.  Hirsch  pointed  out, 
some  years  ago,  that  60°  F.  is  the  limit  at  which  ma- 
larial fevers  can  occur.  Hence  it  happens  that  the 
same  mosquito  may  be  harmless  at  low  temperatures 
and  dangerous  at  higher.  Rainfall  is  important  be- 
cause the  malaria-bearing  mosquito  passes  part  of  its 
life  in  water.  Hence  lakes,  and  especially  marshes, 
pools,  and  swamps  are  critical  controls  as  breeding- 
places  of  the  mosquitoes.  Rain  thus  differs  in  its 
effects  according  to  the  amount  of  precipitation,  and 
according  to  the  conditions  present  where  the  rain 
falls.  A  rain  which  in  one  place  floods  and  scours 
out  mosquito-breeding  pools,  in  another  may  just 
suffice  to  fill  hollows  and  low-lying  places  where 
mosquitoes  may  then  breed.  Digging  up  the  soil, 
whether  for  the  first  time  or  not,  may  result  in  hoi- 


THE  HYGIENE  OF  THE  ZONES  191 

lows  where  puddles  and  pools  may  collect,  and  thus 
give  rise  to  malaria.  The  ground-water  level,  by 
affecting  soil-moisture,  also  plays  a  part,  but  decom- 
posing vegetable  matter  is  no  longer  believed  to  be 
an  essential.  Many  occurrences  or  non-occurrences 
of  malaria,  unexplained  on  any  meteorological 
grounds,  may  be  ascribed  to  the  presence  or  absence 
of  the  malaria-bearing  mosquito. 

The  best  prevention  of  malaria  is  to  screen  persons 
who  have  the  disease,  so  that  they  cannot  infect  mos- 
quitoes, and  to  screen  all  doors  and  windows  so  that 
healthy  individuals  may  not  be  bitten  by  infected 
mosquitoes.  Wholesale  protection  of  this  kind  has 
recently  been  attempted  in  Havana,  on  the  Isthmus 
of  Panama,  in  West  Africa,  and  elsewhere.  The 
danger  of  being  bitten  by  the  Anopheles ,  whose  habits 
are  chiefly  nocturnal,  is  greatest  at  night,  but  resid- 
ence in  tropical  malarial  districts  for  white  persons 
is  always  safest  away  from  native  huts  and  villages. 
The  draining  and  filling  up  of  swamps,  pools,  and 
puddles;  levelling  of  the  surface  of  the  ground;  culti- 
vation of  the  soil  by  planting  trees  or  other  forms  of 
vegetation;  destruction  of  the  larvge  by  pouring  oil 
on  the  standing  waters;  location  of  dwellings  on 
high,  dry  sites;  having  these  dwellings  properly 
screened, — all  these  precautions  should  be  taken. 
Further,  a  rational  and  scientific  use  of  quinine,  and 
a  change  of  climate  to  a  higher  latitude,  are  both  very 
important  measures  in  case  of  the  contraction  of  the 
disease.  Residence  at  an  altitude  of  a  few  thousand 


192  CLIMATE 

feet,  where  the  temperature  is  lower  than  at  sea- 
level,  is  usually  a  sure  preventive,  but  the  mountain 
climates  may  be  injurious  to  persons  suffering  from 
heart  or  lung  troubles,  or  from  rheumatism. 

Relapses  are  very  common  after  a  malarial  attack, 
and  an  anaemic  condition  may  continue  for  a  long 
time.  According  to  Koch,  these  relapsing  cases  in- 
fect the  new  mosquitoes  each  spring,  but  the  same 
authority  believes  it  possible  to  destroy  all  the  para- 
sites in  such  cases,  before  the  spring  comes,  by  the 
use  of  quinine. 

Malaria  is  one  of  the  greatest  obstacles  in  the  way 
of  white  occupation  of  many  tropical  countries. 
Ross  spoke  well  when  he  said  that  the  success  of  im- 
perialism depends  largely  on  success  with  the  micro- 
scope. The  hope  for  the  future  lies  in  the  determined 
effort  to  destroy  the  malaria-bearing  mosquitoes,  and 
to  protect  individuals  from  infection  by  these  mos- 
quitoes. Preventable,  to  a  large  extent,  malaria  cer- 
tainly is,  but  it  is  beyond  the  range  of  human  power 
to  eradicate  the  disease,  certainly  within  any  time 
which  is  of  present  political  interest.  In  the  light 
of  the  new  discoveries,  however,  white  residents  in 
the  tropics  are  now  in  far  less  danger  from  malarial 
infection  than  they  were  a  few  years  ago. 

Yellow  Fever.  Yellow  fever  is  endemic  only  on 
the  eastern  coast  of  the  Americas,  and  on  the  western 
coast  of  Africa,  chiefly  within  the  tropics,  although  it 
frequently  extends  beyond  them,  as  an  epidemic,  even 
to  latitudes  between  40°  and  50°.  It  frequents 


THE  HYGIENE  OF  THE  ZONES  193 

especially  the  squalid  quarters  of  seacoast  towns  and 
the  shores  of  large  navigable  rivers,  readily  follow- 
ing railways,  canals,  and  other  highways  of  travel. 
The  opening  of  the  Panama  Canal  and  the  establish- 
ment of  new  steamship  lines  between  Central  Amer- 
ica and  the  Hawaiian  and  Samoan  Islands,  where 
no  yellow  fever  has  occurred,  may  easily  be  fol- 
lowed by  the  introduction  of  the  disease  into  those 
islands.  Within  the  tropics  the  rainy  season  brings 
the  maximum  prevalence  of  the  disease;  in  extra- 
tropical  latitudes,  the  summer  and  autumn.  Hirsch 
asserts  that  it  has  not  gained  a  foothold  at  tempera- 
tures below  68°  F.  Manson  states  that  a  tempera- 
ture over  75°  F.  is  needed  for  its  development  in 
epidemic  form.  Yellow  fever  weakens  as  cold 
weather  approaches,  and  epidemics  disappear  when 
the  temperature  reaches  32°  F.,  although  the  vitality 
of  the  germ  may  not  be  extinguished  by  frost 
(Manson).  Stations  more  than  a  few  hundred,  or 
thousand,  feet  above  sea-level  are  free  from  the  dis- 
ease, probably  because  of  their  lower  temperatures. 
The  altitude  of  this  zone  varies,  but  at  the  maximum, 
yellow  fever  has  only  very  rarely  occurred  as  high  as 
4000  feet  above  sea-level. 

The  actual  cause  of  yellow  fever  is  still  unknown. 
The  T)rilliant  work  of  Reed,  Carroll,  Agramonte,  and 
Guiteras  has  shown  that  the  intermediate  host,  and 
the  diffusing  agent  of  the  yellow  fever  parasite  is  a 
mosquito  of  the  genus  Stegomyia  fasciata,  which  has 
previously  been  infected  by  biting  a  person  suffering 


194  CLIMATE 

from  yellow  fever.  The  disease  is  non-contagious 
where  S.  fasciata  is  not  present,  as  at  Petropolis, 
near  Rio  de  Janeiro.  Vigorous  campaigns  against 
the  mosquito  have  recently  produced  a  remarkable 
decrease  of  the  disease  at  Havana,  on  the  Isthmus  of 
Panama,  and  at  New  Orleans  in  1905.  The  endemic 
character  of  yellow  fever  in  Rio  is  believed  by 
Manson  to  be  kept  up  by  the  continual  arrival  of 
foreigners  who  are  susceptible  to  the  disease.  New- 
comers are  chiefly  attacked.  After  one  attack,  im- 
munity is  usually  secured.  Persons  who  have  lived 
for  some  time  in  endemic  areas  without  having  the 
fever  are  more  or  less  exempt,  or  may  have  the  dis- 
ease in  mild  form.  The  immunity  of  natives  who 
leave  their  home  decreases  with  the  length  of  their 
absence.  Negroes  enjoy  comparative  immunity;  the 
yellow  race  is  more,  and  the  white  race  most,  suscep- 
tible. Of  the  white  race,  northerners  are  more  sus- 
ceptible than  southerners. 

Dysentery:  Diarrhoea!  Disorders.  Dysentery  oc- 
curs epidemically  in  all  latitudes,  but  has  its  home  in 
the  warmer  climates,  as  a  whole  increasing  in  severity 
and  frequency  with  approach  to  the  equator.  Some 
form  of  dysentery  is  almost  always  present  in  lower 
latitudes,  where  this  disease  is  next  in  importance  to 
malaria  in  causing  high  death-rates  and  in  its  lasting 
effects.  High  temperatures  are  clearly  necessary 
for  the  development  of  the  disease  germ,  but  numer- 
ous other  controls  are  also  needed.  The  maximum 
is  usually  in  the  hottest,  or  wettest,  months;  cooler 


THE  HYGIENE  OF  THE  ZONES  195 

weather  checks  the  disease.  In  India,  the  latter  half 
of  the  rainy  season  shows  the  maximum.  Altitude 
cannot  be  relied  on  to  give  relief  from  dysentery; 
residents  on  mountains  often  suffer  more  than  those 
at  lower  levels.  Lack  of  sanitary  precautions,  im- 
pure water,  overcrowding,  poor  food,  excesses  of  all 
kinds,  are  predisposing  causes.  The  best  preventive 
is  a  rational,  temperate  mode  of  life ;  protection  of  the 
more  susceptible  parts  of  the  body  against  chills,  and 
a  proper  regulation  of  the  whole  system.  Epidem- 
ics of  dysentery  seem  independent  of  the  effects  of 
wind,  rain,  and  atmospheric  humidity.  Immunity 
is  not  secured  after  one  attack,  several  attacks  being 
common. 

In  extra-tropical  latitudes,  diarrhoeal  disorders 
show  a  similar  dependence  on  temperature,  for  they 
are  most  frequent  in  summer  and  early  autumn. 
Usually  the  hotter  the  summer,  the  greater  the  pre- 
valence and  the  severity  of  these  complaints,  and  the 
higher  the  death-rate  from  them.  Other  factors  are, 
however,  concerned  in  this  matter,  so  that  "  all  at- 
tempts to  express  the  diarrhoeal  mortality  of  a  given 
place  as  a  function  of  the  temperature  only  have 
failed."  Soil  temperature  is  one  factor  between 
which  and  the  death-rate  from  diarrhoeal  disorders 
some  relation  has  been  made  out. 

Tropical  Abscess  of  the  Liver.  Rare  in  temper- 
ate and  cool  climates,  tropical  abscess  of  the  liver,  as 
the  name  implies,  is  mainly  a  disease  of  warmer  lati- 
tudes and  usually  accompanies  or  follows  dysentery. 


196  CLIMATE 

Among  the  predisposing  causes  the  most  potent  are 
injudicious  and  intemperate  habits,  especially  over- 
eating and  over-indulgence  in  alcoholic  beverages; 
insufficient  exercise;  exposure;  chills,  and  in  general 
the  "  congestive  and  degenerative  conditions  inciden- 
tal to  tropical  life."  Heat,  malaria,  and  dysentery 
are  active  precursors  of  liver  abscess,  in  that  they 
lower  the  vitality.  The  disease  is  most  common  dur- 
ing the  colder  or  rainier  season,  when  chills  are  most 
frequent,  but  temperature  is  not  the  sole  control. 
The  physiological  adjustment  of  a  person  from  a 
colder  latitude  to  tropical  conditions  of  climate  throws 
a  considerable  strain  upon  the  liver.  The  result, 
especially  if  intemperate  living  is  indulged  in,  is 
likely  to  be  liver  abscess.  Chiefly  because  of  their 
disregard  of  proper  hygiene,  white  men  and  women 
are  generally  more  liable  to  have  the  disease  than  na- 
tives ;  the  death-rate  among  white  troops  in  the  tropics 
is  much  higher  than  among  native  troops  in  the  case 
of  this  disease.  Tropical  liver  abscess  is  most,  but 
by  no  means  solely,  to  be  expected  in  the  earlier  years 
of  residence  in  the  tropics.  Persons  suffering  from 
the  disease  should,  if  possible,  be  sent  to  a  temperate 
climate,  although  there  are  many  cases  of  recovery 
even  in  the  tropics. 

Cholera.  Cholera  is  due  to  the  specific  microbe, 
the  comma  bacillus,  discovered  by  Koch  in  1883. 
From  its  home  in  India,  it  has  spread  in  great  wraves 
as  an  epidemic  over  most  of  the  globe,  the  last  ad- 
vance reaching  its  maximum  extension  early  in  the 


THE  HYGIENE  OF  THE  ZONES  197 

decade  1890-1900,  in  northern  Europe.  Cholera 
has  gone  as  far  north  as  Bergen  in  Norway,  and  in 
Siberia  up  to  about  latitude  60°  N.  No  general  re- 
lations can  be  established  between  the  occurrence  of 
cholera  and  climatic  or  weather  conditions.  Local 
conditions  exercise  an  important  control.  In  higher 
latitudes,  however,  cholera  seems  most  frequent  to- 
wards autumn,  decreasing  with  falling  temperatures. 
Cholera  is  chiefly  prevalent  in  low-lying  places,  on 
river  banks,  and  where  human  beings  are  over- 
crowded under  unsanitary  conditions.  The  at- 
mosphere is  clearly  not  the  agent  for  carrying  the 
bacillus,  for  the  latter  does  not  keep  its  morbific  char- 
acter long  in  the  free  air.  The  principal  agent  in 
spreading  the  disease  is  traffic;  but  drinking-water 
certainly  also  plays  a  part.  As  a  whole,  cholera  is 
rarer  and  milder  in  the  higher  latitudes,  and  has  de- 
creased in  Europe  in  cold  weather,  coming  up  again 
in  summer.  It  has,  however,  also  been  active  at  low 
temperatures.  With  many  exceptions,  there  may  be 
said  to  be  a  decrease  with  altitude,  and  soil  moisture 
may  also  play  a  part. 

Plague.  The  specific  cause  of  plague  is  a  bacillus 
discovered  by  Kitasato,  a  pupil  of  Koch,  in  1894,  and 
also  independently  by  Yersin.  Formerly  very  wide- 
spread, plague  is  now  confined  to  the  sub-tropical  dis- 
tricts of  southern  Asia  and  of  the  Mediterranean. 
It  has  become  a  disease  of  warm  climates,  because 
it  depends  upon  the  unsanitary  conditions  in  which 
tropical  natives  live,  and  it  attacks  the  poorer  part  of 


198  CLIMATE 

the  population.  Filth,  famine,  social  misery,  and 
overcrowding  are  predisposing  causes.  The  con- 
clusions regarding  the  relation  of  plague  to  weather 
and  climate  are  almost  as  numerous  as  are  those  who 
have  investigated  this  subject,  but  it  is  clear  that 
plague  is  not  limited  by  isotherms,  and  that  meteoro- 
logical conditions  do  not  spread  it,  or  solely  control 
it.  The  Indian  Plague  Commission  concludes  that 
there  is  no  direct  connection  between  plague  and 
climate;  Hirsch  had  previously  stated  that  the  rela- 
tion is  unsettled.  In  the  tropics,  however,  the  dis- 
ease has,  on  the  whole,  had  a  cool  season,  and  in 
higher  latitudes  a  warm  season,  maximum.  As  to 
altitude,  plague  has  occurred  at  high  levels  in  cold, 
dry  climates,  and  at  low  levels  where  the  climate  is 
warm  and  moist.  It  has  prevailed  when  the  tem- 
peratures were  so  low  that  people  suffered  with  the 
cold  (Roumelia,  1737-8),  and  at  temperatures  so 
high  that  sunstrokes  occurred  (Smyrna,  1735). 
On  the  whole,  plague  has  chiefly  prevailed  under 
moderately  high  temperature  and  moisture  condi- 
tions, and  where  the  soil  is  damp  and  the  ground  low. 
These  facts  do  not,  however,  necessarily  point  to 
cause  and  effect. 

The  best  preventives  of  plague  are  pure  air  and 
modern  sanitation.  In  India,  Haffkine  has  been 
very  successful  with  inoculation.  Plague  travels  by 
trade  routes.  Persons  sick  with,  or  incubating 
plague,  and  infected  clothing  and  personal  effects, 
carry  the  infection. 


TEE  HYGIENE  OF  THE  ZONES  199 

rSimstroke  and  Related  Conditions.  Several  dis- 
agreeable and  some  fatal  results  of  heat  and  hu- 
midity, not  to  be  classed  as  diseases,  are  common  in 
the  tropics,  and  to  a  considerable  extent  also  in  extra- 
tropical  latitudes,  even  as  far  as  latitude  50°  to  60° 
N.  Sunstroke  and  heat  prostration  are  most  com- 
mon in  the  tropics  when  the  air  is  damp  during  calms, 
and  in  temperate  latitudes  during  the  hottest  spells 
of  summer,  when  the  weather  conditions  are  tropical 
in  character.  The  germ  origin  of  sunstroke  has 
been  maintained  by  Sambon,  but  the  cause  is  to  be 
found  in  the  effects  of  insolation,  direct  and  reflected ; 
the  air  temperatures,  and  the  undue  heating  of  the 
body.  The  skin  of  white  persons  when  exposed  to 
the  sun  in  the  tropics  often  becomes  burned  and 
blistered,  and  travellers  commonly  suffer  because  of 
lack  of  protection  of  neck  or  limbs  under  sunshine. 
Exposure  to  the  sun  does  not  always  explain  sun- 
stroke, for  at  sea  the  tropical  sun  is  less  fatal  than  on 
land,1  and  places  with  apparently  similar  conditions 
of  insolation  differ  much  as  regards  the  prevalence  of 
sunstroke.  A  great  deal  doubtless  depends  on  oc- 
cupation. Many  forms  of  heat  exhaustion  are  in- 
duced by  exposure  to  high  temperatures,  but  greatly 
aggravated  by  unsuitable  clothing,  impaired  physical 
condition,  and  intemperance. 

A   study   of   the   sunstroke   weather   of   August, 
1896,  in  the  United  States,  led  Dr.  W.  F.  R.  Phillips 

1  Stokers  and  firemen  suffer  from  prostration  on  steamers  in  the 
tropics,  but  here  artificial  heat  is  partly  responsible. 


200  CLIMATE 

to  conclude  that  the  number  of  sunstrokes  followed 
the  excess  of  the  temperature  above  the  normal  more 
closely  than  it  did  any  other  meteorological  element; 
that  there  was  no  definite  relation  to  the  relative  or 
absolute  humidity;  and  that  the  liability  to  sunstroke 
increased  in  proportion  as  the  mean  temperature  of 
any  day  approached  the  normal  maximum  tempera- 
ture for  that  day. 

Sunstroke  is  most  common  among  those  who  are 
exposed  to  the  sun,  and  at  hard  work  under  condi- 
tions which  retard  or  check  the  cooling  of  the  body 
by  radiation  or  conduction.  The  best  protection 
against  sunstroke  and  heat  prostration  in  general, 
and  especially  in  the  tropics,  is  to  be  found  in  the  use 
of  suitable  light  and  loose  clothing;  loose,  wide- 
brimmed,  and  well-ventilated  headgear;  avoidance  of 
exposure  to  sun  and  to  high  temperatures  in  general; 
the  use  of  a  white  umbrella ;  avoidance  of  alcohol  and 
of  an  excess  of  heating  foods,  and  in  a  temperate  life 
in  all  respects.  Poor  health,  fatigue,  and  violent  ex- 
ercise are  all  predisposing  causes.  Tropical  camps 
should  be  located  in  cool  and  well-ventilated  places, 
and  tents  should  have  double  roofs. 

Dengue.  Dengue  is  a  "  highly  infectious,  febrile 
disease,  characterised  by  severe  rheumatoid  pains  in 
joints  and  limbs,  and  in  some  cases  by  a  cutaneous 
eruption  of  varying  character  and  duration."  It  is 
distinctly  a  disease  of  warm  climates,  although  it  has 
occurred  as  far  north  as  latitude  40°  in  Europe  and 
in  North  America,  and  as  far  south  as  the  southern 


THE  HYGIENE  OF  THE  ZONES  201 

tropic.  It  comes  mostly  in  the  hottest  months,  and 
is  almost  always  checked  by  cold  weather.  Moisture 
has  a  subordinate  influence.  Dengue  resembles  yel- 
low fever  in  its  prevailing  preference  for  coasts, 
deltas,  and  large  river  valleys;  in  its  relation  to  over- 
crowding and  unsanitary  conditions,  and  in  its  ad- 
vance along  routes  of  travel.  Dengue  attacks  any 
race,  and  immunity  is  not  secured  by  one  attack. 
There  is  often  a  recurrence. 

Beri-beri.  A  dropsical  affection,  combined  with  a 
disturbance  of  motion  and  sensation,  and  of  heart 
action,  beri-beri  is  found  principally  in  or  near 
the  tropics,  being  especially  common  in  the  Malay 
Peninsula,  and  the  adjacent  archipelago,  where  it  is 
often  a  scourge.  It  is  especially  liable  to  break  out 
among  gangs  of  labourers.  Beri-beri  epidemics  are 
most  common  during  the  rainy  season.  High  tem- 
perature and  dampness  are  controlling  factors,  as  are 
poor  health,  fatigue,  privation,  chill,  overcrowding, 
etc.  Damp  years  are  apt  to  be  marked  by  the  sever- 
ity and  prevalence  of  beri-beri. 

Other  Tropical  Diseases.  Among  other  tropical 
diseases  may  be  named  sleeping  sickness,  limited  to 
tropical  Africa  and  attacking  both  native  negroes  and 
whites;  and  yaws,  also  distinctly  tropical  in  distribu- 
tion, requiring  high  temperature  and  moisture,  found 
chiefly  in  some  of  the  larger  island  groups,  and  prin- 
cipally affecting  the  negro. 

General  Conclusions:  Tropics.  All  parts  of  the 
equatorial  zone  are  not  equally  disagreeable  or  hostile, 


202  CLIMATE 

so  far  as  occupation  by  the  white  race  is  concerned. 
Many  elderly  persons  and  those  who  are  overworked 
may  find  rest  from  nervous  tension  in  the  enervating 
climate  of  the  tropics.  The  drier  districts  are  to  be 
preferred  to  the  moister,  the  higher  altitudes  to  the 
lowlands,  coasts  and  islands  well  ventilated  by  pre- 
vailing winds,  to  regions  where  the  air  is  stagnant. 
Much-needed  relief  from  the  heat  at  sea-level  may 
be  obtained  by  resort  to  tropical  mountain  stations, 
and  many  of  these  have  become  well-known  health 
resorts.  Tropical  mountain  climates  resemble  the 
climate  of  the  temperate  zones  in  their  lower  tem- 
peratures and  in  certain  other  ways,  but  they  can 
never  be  the  equivalent  of  a  temperate  zone  climate, 
for  they  lack  the  seasonal  changes.  Some  tropical 
climatic  characteristics  disappear  with  altitude,  while 
1  others  change  little.  The  non-seasonal  character  of 
tropical  mountain  climates,  the  so-called  "  perpetual 
spring,"  is  not  by  any  means  the  best  fitted  for  man's 
physical  and  mental  development,  however  pleasant 
it  may  be  for  a  time.  With  increase  of  altitude,  there 
is  a  decrease  in,  or  a  disappearance  of,  some  of  the  dis- 
eases which  prevail  near  sea-level,  such  as  malaria, 
yellow  fever,  liver  abscess,  etc.  When  introduced 
from  the  lowlands,  such  diseases  are  not  likely  to  be 
severe,  or  to  spread.  In  their  stead,  however,  may 
come  an  increasing  frequency  of  diseases  which  are 
characteristic  of  high  latitudes,  such  as  rheumatism, 
and  heart  and  lung  troubles.  Tropical  hill  stations 
in  India  show  a  smaller  mortality  among  the  troops 


THE  HYGIENE  OF  THE  ZONES  203 

than  do  lower  levels.  In  India,  as  elsewhere  in  the 
tropics,  hill  stations  are  beneficial  in  restoring  those 
who  are  exhausted  by  overwork  or  by  the  heat  of  the 
lowlands.  They  are  especially  advantageous  for 
delicate  women  and  children.  Nevertheless,  climates 
which  are  temperate  because  of  altitude  in  the  tropics 
cannot  replace  climates  wrhich  are  "  temperate  "  be- 
cause of  latitude. 

The  acclimatisation  of  the  white  race  in  the  tropics 
is  a  question  of  vast  importance.  Upon  it  depend 
the  control,  government,  and  utilisation  of  the  tropics. 
It  is  a  very  complex  problem,  and  it  has  been  much 
discussed.  It  is  complicated  by  the  controls  exercised 
by  race,  diet,  occupations,  habits  of  life,  and  the  like. 
To  discuss  it  fully  is  impossible  in  this  place.  The 
gist  of  the  matter  is  this :  White  residents  from  cooler 
latitudes  on  coming  into  the  tropics  must  adjust 
themselves  physiologically  to  the  new  climatic  condi- 
tions. During  this  adjustment  there  is  more  or  less 
strain  on  various  organs  of  the  body.  The  strain 
may  be  too  severe;  then  the  individual  suffers.  The 
adjustment  is  usually  much  retarded  and  hindered  by 
a  persistence  in  habits  of  food,  drink,  and  general 
mode  of  life  which,  however  well  suited  to  the  home 
climate,  do  not  fit  tropical  conditions.  During  the 
adjustment,  especially  if  complicated  by  irrational 
habits,  the  body  is  naturally  sensitive  to  the  new  dis- 
eases to  which  it  is  exposed.  Even  should  no  specific 
disease  be  contracted,  there  are  ansemic  tendencies  and 
other  degenerative  changes.  Experience  teaches 


204  CLIMATE 

that  white  men  cannot  with  impunity  do  hard  man- 
ual labour  under  a  tropical  sun,  but  that  they  may 
enjoy  fairly  good  health  as  overseers,  or  at  indoor 
work,  if  they  take  reasonable  precautions.  Accli- 
matisation in  the  full  sense  of  having  white  men  and 
women  living  for  successive  generations  in  the  tropics, 
and  reproducing  their  kind  without  physical,  mental, 
and  moral  degeneration, — i.  e.,  colonisation  in  the 
true  sense, — is  impossible.  Tropical  disease  and 
death-rates,  as  has  been  abundantly  shown,  can  be 
much  reduced  by  proper  attention  to  sanitary  laws, 
so  that  these  rates  may  be  not  much,  if  any,  higher 
than  those  in  the  extra-tropics.  And  with  increas- 
ing medical  knowledge  of  the  nature  and  prevention 
of  tropical  diseases,  as  well  as  by  means  of  modern 
sanitary  methods,  a  white  resident  in  the  tropics  will 
constantly  become  better  able  to  withstand  disease. 
As  Manson  has  put  it,  acclimatisation  is  less  "  an 
unconscious  adaptation  of  the  physiology  of  the 
individual "  than  "  an  intelligent  adaptation  of  his 
habits."  For  greater  comfort,  for  better  health,  and 
for  greater  success,  properly  selected  hill  stations 
will,  however,  always  be  essential  to  northerners  who 
have  to  live  in  the  tropics,  especially  to  white  women 
and  children. 

It  has  been  well  said  that  the  white  soldier  in  the 
tropics  is  "always  in  campaign;  if  not  against  the 
enemy,  at  least  against  the  climate."  This  sentence 
may  be  made  to  fit  the  case  of  the  white  civilian  in 
the  tropics  by  making  it  read:  the  white  race  in  the 


TEE  HYGIENE  OF  THE  ZONES  205 

tropics  is  always  in  campaign  against  its  enemy,  the 
climate. 

Temperate  Zones:  General.  Far  from  being 
temperate  as  regards  the  general  climatic  conditions 
over  much  of  the  land  area  of  the  so-called  temper- 
ate zones,  these  belts  rightly  deserve  their  name  only 
in  the  sense  that  in  their  physiological  effects  they  are 
intermediate  between  the  equatorial  and  the  polar 
zones.  In  the  temperate  zones  the  organs  of  the 
body  act  more  equally  than  in  the  warmer  or  the 
cooler  latitudes.  In  the  central  part  of  the  temper- 
ate zones,  especially  over  the  continents,  are  found 
the  four  seasons.  The  winter  cold  is  met  by  means 
of  warm  clothing,  heated  houses,  and  other  means  of 
protection.  Unless  too  severe,  or  too  prolonged,  when 
deaths  by  freezing  may  occur,  the  cold  of  a  continen- 
tal winter  in  the  north  temperate  zone  acts  as  a  health- 
ful stimulant  upon  body  and  mind.  In  the  tropics, 
the  body  is  unused  to  adjusting  itself  to  tempera- 
ture changes,  because  such  changes  are  there  slight, 
and  is  readily  affected  by  them.  But  the  frequent, 
sudden,  and  severe  changes  of  many  parts  of  the  tem- 
perate zone  are  usually  borne  without  serious  dis- 
comfort or  injury,  if  the  body  is  in  good  health,  and 
is  accustomed  to  adjusting  itself  readily  to  these 
changes.  The  habit  of  keeping  houses  very  warm 
during  the  winter,  and  of  having  the  air  indoors  very 
dry,  weakens  the  body's  power  to  resist  the  great  cold 
outdoors,  especially  if  the  air  be  damp,  and  causes 
affections  of  throat,  lungs,  and  nose.  The  summers, 


206  CLIMATE 

although  hot  in  the  lower  latitudes  of  these  zones, 
and  marked  by  spells  of  warm  weather  even  to  their 
polar  limits,  are  not  characterised  by  such  steady, 
uniformly  moist  heat  as  is  typical  of  the  tropics. 
When  the  heat  is  extreme,  and  the  relative  hu- 
midity is  high,  night  and  day,  sunstroke  and  kin- 
dred affections  are  occasionally  noted  in  places, 
but  the  invigorating  cool  of  autumn  and  winter  are 
never  far  off,  and  may  always  be  trusted  to  bring 
relief. 

Winter  and  Summer  Diseases.  It  is  natural  that 
marked  seasonal  and  sudden  weather  changes,  such 
as  those  which  characterise  much  of  the  temperate 
zones,  especially  in  the  northern  hemisphere,  should 
be  reflected  in  the  character,  distribution,  and  fre- 
quency of  the  diseases  which  are  found  in  these  zones. 
Diseases  of  the  respiratory  system,  bronchial  and 
rheumatic  affections,  diseases  that  result  from  colds 
and  chills,  pneumonia,  bronchitis,  influenza,  diphthe- 
ria, whooping  cough,  are  all  common  in  climates  with 
sudden  marked  temperature  changes,  especially  if 
those  changes  are  accompanied  by  cold,  damp  winds. 
These  diseases  are  also  most  frequent  in  the  winter 
months,  when  the  weather  changes  are  more  common 
and  more  severe,  and  when,  in  consequence,  the  vital- 
ity of  the  body  is  lowered  and  its  power  of  resistance 
against  the  attack  of  disease  germs  is  weakened.  A 
greater  prevalence  of  diseases  of  the  respiratory  or- 
gans, catarrhs,  and  rheumatic  affections  in  cool,  moist 
wreather,  with  sudden  changes,  has  been  shown  by 


THE  HYGIENE  OF  THE  ZONES  207 

Weber,  and  several  investigators  have  found  a  higher 
mortality  after  a  greater  variability  of  temperature. 
Many  contagious  or  infectious  diseases,  such  as  diph- 
theria, influenza,  measles,  and  scarlet  fever,  for  ex- 
ample, are  also  more  common  in  the  colder  season,  not 
because  the  lower  temperatures  are  the  direct  control- 
ling factor,  but  largely  because  the  colder  weather 
drives  people  indoors ;  houses  and  buildings  generally 
are  less  well  ventilated;  more  clothing  is  worn,  less 
attention  is  paid  to  personal  cleanliness,  and  there 
is  increased  opportunity  for  contagion,  especially 
among  the  poorer  classes.  Obviously,  these  are  in- 
direct effects  of  meteorological  conditions.  Other 
factors,  also,  must  be  taken  into  consideration.  Thus 
one  reason  why  the  natives  of  the  farther  north,  where 
the  winters  are  very  severe,  suffer  less  from  some  of 
the  diseases  which  are  common  in  warmer  latitudes 
is  not  because  of  the  lower  temperatures,  but  because 
they  are  less  exposed  to  contagion  owing  to  less  com- 
munication with  the  outside  world. 

In  the  warmer  months,  fevers  and  diseases  of  the 
digestive  system,  diarrhoea,  malaria,  typhoid  fever, 
are  prevalent.  Thus  there  are  usually  two  maxima 
of  mortality :  one  in  the  colder  season,  when  the  vari- 
ability of  temperature  is  greatest,  chiefly  due  to  re- 
spiratory diseases,  and  another  in  the  warmer  months, 
largely  due  to  infant  mortality  from  diarrhoeal 
disorders. 

Tuberculosis.  "  A  nationally  self-inflicted,  un- 
necessary, and  preventable  pestilence  " ;  world-wide 


208  CLIMATE 

in  extent;  found  in  every  variety  of  climate,  and  at 
all  altitudes;  causing  from  10  to  15  per  cent,  of  all 
deaths;  the  scourge  of  the  temperate  zone,  tuber- 
culosis is,  on  the  whole,  less  frequent  in  higher 
latitudes,  on  mountains,  and  in  arid  or  semi-arid  dis- 
tricts. Climate,  however,  is  not  the  controlling  fac- 
tor in  the  latter  cases,  but  sparseness  of  population 
and  infrequency  of  communication  with  the  outside 
world.  The  density  of  population;  the  social  and 
economic  conditions;  the  occupations  and  habits  of 
the  people, — these  are  important  controls.  Over- 
crowding amid  unsanitary  surroundings,  absence  of 
sunlight,  impure  air,  are  predisposing  causes. 
Weather,  or  other  conditions  which  decrease  the  vi- 
tality, increase  the  susceptibility  to  tuberculosis. 
Sudden  temperature  changes,  especially  with  high 
relative  humidity  at  low  temperatures,  cause  chills 
and  lower  vitality. 

Consumption,  it  is  clear,  can  be  successfully  treated 
where  pure  air,  abundant  sunshine,  good  food,  and 
outdoor  exercise  are  to  be  had.  The  first  of  these 
desiderata,  pure  air,  and  plenty  of  it,  is  the  most  im- 
portant of  all.  It  is  usually  found  on  desert,  ocean, 
mountain,  and  in  forest.  Hence  such  climates  are 
generally  advantageous  in  the  treatment  of  tuber- 
culosis of  various  kinds.  Yet  climate  is  no  longer 
believed  to  play  as  important  a  role  in  the  matter 
as  was  formerly  assigned  to  it.  Good  hygiene  has 
to  a  large  extent  replaced  climate.  A  health  resort 


THE  HYGIENE  OF  THE  ZONES  209 

where  a  patient  can  find  comfortable  quarters,  con- 
genial company,  plenty  of  diversion,  and  where 
favourable  climatic  conditions,  such  as  abundant  sun- 
shine, absence  of  disagreeable  winds,  dust,  and  sudden 
weather  changes,  encourage  outdoor  life,  is  to  be 
recommended.  The  climate  does  not  cure;  it  is  an 
important  help  in  the  treatment  of  the  disease.  Some 
patients,  especially  elderly  people  and  those  suffer- 
ing from  nervous,  cardiac,  or  bronchial  affections, 
fare  better  at  lower  altitudes;  but  higher  altitudes, 
with  the  stimulating  effects,  deep  respiration,  and  ac- 
tive use  of  the  lungs  which  they  induce,  often  offer 
many  climatic  conditions  favourable  to  outdoor  life 
and  hence  of  great  benefit  in  the  treatment  of  the 
disease.  The  dry,  pure  air  and  abundant  sunshine 
of  many  of  the  well-known  mountain  health  resorts 
are  very  favourable  climatic  helps.  Moreover,  the 
smaller  temperature  ranges  of  mountain  and  marine 
climates  are  also  helpful.  In  many,  if  not  in 
most  cases,  any  change  of  climate  is  beneficial,  but 
especially  so  if  such  a  change  is  accompanied  by  the 
favourable  conditions  just  enumerated.  Ocean  air, 
although  damp,  is  beneficial  to  many  patients  because 
of  its  purity,  its  salinity,  and  its  small  temperature 
ranges.  Hence  an  ocean  voyage,  with  its  relief  from 
unsanitary  or  harmful  occupations,  may  be  an  ex- 
cellent restorative.  Results  obtained  in  the  treat- 
ment of  tuberculosis  by  climatic  change  vary  through 
a  wide  range.  The  reasons  for  such  discrepancy  are 


210  CLIMATE 

to  be  sought  in  the  difference  in  the  stage  of  the  dis- 
ease treated,  and  in  the  habits,  food,  and  mode  of  life 
of  the  patients. 

Pneumonia.  Pneumonia  is  found  almost  every- 
where, in  the  tropics  probably  quite  as  commonly  as 
in  colder  latitudes,  and  at  high  altitudes  as  well  as  at 
sea-level.  A  greater  frequency  of  pneumonia  gen- 
erally follows  cold,  damp  weather,  with  marked 
changes  of  temperature,  which  lower  the  vitality  and 
are  conducive  to  chills.  Hence  the  disease  is  most 
prevalent  in  the  colder  months.  Among  the  predis- 
posing causes,  physical  weakness  following  other  dis- 
eases is  potent,  as  are  mal-nutrition  and  similar 
debilitating  agencies.  Severe  cold  spells  are  likely 
to  be  followed  by  an  increase  of  pneumonia,  espe- 
cially among  elderly  persons  and  children.  Negroes 
who  have  gone  to  cold  climates  are  very  subject  to 
the  disease. 

Diphtheria.  Although  geographically  widely  dis- 
tributed, diphtheria  is  chiefly  a  temperate  zone  dis- 
ease, occurring  sporadically  or  epidemically,  however, 
in  tropics  and  polar  latitudes.  Like  other  infectious 
diseases  of  the  temperate  zone,  diphtheria  is  most 
frequent  in  the  colder  months,  because  the  conditions 
of  life  are  then  most  favourable  to  contagion,  and 
because  vitality  is  then  most  lowered  by  the  prevail- 
ing weather  conditions.  Diphtheria  is  more  common 
at  low  altitudes  than  high. 

Influenza.  The  well-known  disease,  "  grippe," 
caused  by  a  specific  organism  discovered  in  1892,  is 


THE  HYGIENE  OF  THE  ZONES  211 

occasionally  very  serious,  and  is  apt  to  be  closely 
followed  by  epidemics  of  pneumonia  and  other  dis- 
eases of  the  respiratory  organs.  Although  very 
carefully  studied,  there  is  no  certain  evidence  of  any 
influence  of  weather,  climate,  or  soil  upon  the  disease. 
The  last  great  epidemic  of  influenza,  in  1890  and 
thereabout,  is  believed  by  Assmann  to  have  been 
associated  with  dry  spells  and  with  the  carriage  of 
dust.  The  worst  outbreaks  have  been  in  the  colder 
season,  when  indoor  life,  less  fresh  air,  and  overcrowd- 
ing would  naturally  help  to  spread  the  contagion. 
The  fact  that  those  who  are  suffering  from  influenza 
are  often  not  kept  indoors  explains  a  general  spread 
of  the  disease. 

Bronchitis.  Bronchitis  is  most  common  in  the 
higher  latitudes,  and  in  the  cold  months,  when  the 
temperature  is  low  and  when  sudden  and  rapid  varia- 
tions of  temperature  are  frequent.  Dust,  blown  from 
the  dry  surface  of  streets  and  the  like,  helps  to  irritate 
the  throat  and  nasal  passages.  Relief  from  bron- 
chitis may  be  found  where  the  climate  is  wrarm  and 
uniform;  the  air  soft  and  balmy;  where  there  are  no 
irritating  winds  driving  the  dust  to  and  fro,  and 
where  sunshine  is  abundant. 

Rheumatism.  Rheumatic  affections  are,  as  a  whole, 
more  common  in  colder  than  warmer,  and  in  damper 
than  drier  climates,  but  may  be  classed  under  the 
temperate  zone.  Exposure  to  cold  and  wet,  bring- 
ing on  chills,  and  sudden  temperature  changes,  es- 
pecially in  damp  climates,  while  not  the  cause  of 


212  CLIMATE 

rheumatism  lowers  the  vitality  in  such  a  way  that  the 
specific  cause  may  assert  itself.  In  many  cases  a 
change  of  altitude  makes  no  difference  whatever;  it 
may,  in  fact,  aggravate  the  trouble. 

Measles  and  Scarlet  Fever.  Both  measles  and 
scarlet  fever  are  independent  of  weather  and  climate, 
except  in  so  far  as  the  colder,  more  inclement,  months 
involve  an  unhealthier  mode  of  life,  with  less  atten- 
tion to  sanitary  measures.  A  maximum  is  usually 
found  in  the  colder  months,  when  infection  is  most 
likely.  Measles  occurs  in  all  climates,  but  usually 
most  commonly  and  most  severely  in  temperate  lati- 
tudes. Scarlet  fever  is  essentially  a  disease  of  the 
temperate  zone.  Isolation  from  sources  of  infection 
is  more  important  than  any  climatic  control  in  these 
diseases,  which  show  very  various  relations  to  season, 
altitude,  and  race. 

Typhoid  Fever.  Typhoid  fever  is  found  in  al- 
most all  parts  of  the  world.  Although  common  in 
the  tropics,  being  one  of  the  most  generally  fatal 
diseases  there,  especially  among  recent  European 
arrivals,  it  is  not,  according  to  Manson,  properly 
classified  as  a  tropical  disease.  It  is  very  prevalent  in 
the  temperate  zone,  having  a  maximum  frequency  in 
late  summer  and  autumn,  and  is  certainly  largely 
preventable  by  good  sanitation  and  pure  food  and 
water.  The  germs  of  typhoid  fever  are  killed  in  a 
few  hours  under  direct  sunshine,  and  their  growth  is 
slow  even  in  diffused  daylight.  The  well-known 
studies  of  Pettenkofer,  at  Munich,  showed  an  inverse 


THE  HYGIENE  OF  THE  ZONES  213 

relation  between  the  ground-water  level  and  the  pre- 
valence of  typhoid,  but  this  appears  not  to  be  a 
universal  relation.  The  view  formerly  held  regard- 
ing a  connection  between  temperature  and  humidity 
and  typhoid  epidemics  has  now  generally  been 
abandoned. 

Whooping  Cough.  Whooping  cough  is  more 
prevalent  in  temperate  and  cooler  climates,  where  the 
temperature  changes  are  marked  and  where  the 
respiratory  organs  are  most  affected,  and  is  rare  and 
less  severe  in  warmer  latitudes.  But  the  absence  of 
whooping  cough  is  doubtless  often  to  be  explained 
on  the  ground  that  it  has  not  been  imported,  rather 
than  on  any  direct  climatic  basis.  Although  com- 
moner and  more  severe  in  the  cooler  months,  epi- 
demics may  occur  at  all  times,  without  relation  to 
altitude.  Croup,  also,  prevails  chiefly  in  damp,  cool 
weather,  with  sudden  changes. 

Cholera  Infantum.  Among  the  summer  diseases 
of  the  temperate  zone,  cholera  infantum  occupies  a 
very  prominent  place.  It  increases  with  rising,  is  at 
a  maximum  with  maximum,  and  decreases  with  fall- 
ing, temperatures.  The  greater  and  more  continu- 
ous the  heat,  the  more  general  is  the  disease.  Cool 
spells  check  it  immediately.  It  is  more  common  in 
the  overcrowded  and  overheated  quarters  of  the  city 
than  in  the  country,  and  may  be  greatly  checked  by 
the  use  of  pure  milk  and  fresh  food. 

Hay  Fever.  The  specific  cause  of  hay  fever  has 
been  much  debated,  but  is  generally  regarded  as 


214  CLIMATE 

vegetable  pollen  of  some  sort.  The  particular  kind 
of  pollen  may  differ  in  different  cases.  The  irrita- 
tion is  naturally  confined  to  the  season  of  plant 
growth.  Relief  may  generally  be  secured  by  seek- 
ing a  higher  altitude,  where  the  cause  of  irritation  is 
absent,  and  where  the  air  is  pure  and  clean.  Sea 
voyages,  also,  are  beneficial. 

Polar  Zones:  General.  The  north  polar  summer, 
as  has  been  pointed  out,  in  spite  of  its  drawbacks,  is 
in  some  respects  a  pleasant  and  healthful  season. 
But  the  polar  night  is  monotonous,  depressing,  re- 
pelling. Parry  said  that  it  would  be  difficult  to  con- 
ceive of  two  things  which  are  more  alike  than  two 
polar  winters.  An  everlastingly  uniform  snow  cov- 
ering, rigidity,  lifelessness,  silence — except  for  the 
howl  of  the  gale  or  the  cracking  of  the  ice.  Small 
wonder  that  man  feels  like  an  intruder.  Small  won- 
der that  the  polar  night  has  sometimes  unbalanced 
men's  minds.  Extraordinarily  low  winter  tempera- 
tures are  easily  borne  if  the  air  be  dry  and  still.  Nan- 
sen  notes  "  not  very  cold  "  at  a  temperature  of  -  -  22°, 
when  the  air  was  still.  Another  Arctic  explorer,  at 
-  9°,  says  "it  is  too  warm  to  skate."  Zero  weather 
seems  pleasantly  refreshing  if  clear  and  calm.  But 
high  relative  humidity  and  wind — even  a  light  breeze 
—give  the  same  degree  of  cold  a  penetrating  feeling 
of  chill  which  may  be  unbearable.  Thus  the  damper 
air  of  spring  and  summer  usually  seems  much  colder 
than  the  drier  air  of  winter,  although  the  temperatures 
may  be  the  same.  Large  temperature  ranges  are 


THE  HYGIENE  OF  THE  ZONES  215 

endured  without  danger  in  the  polar  winter  when  the 
air  is  dry.  When  exposed  to  direct  insolation,  the 
skin  burns  and  blisters;  the  lips  swell  and  crack.  In 
severe  cold  the  vitality  of  the  body  is  lowered,  the 
pulse  slackened,  and  the  ability  to  bear  hardships  de- 
creased. The  surface  of  the  body  cools  first;  the 
blood  circulates  more  slowly;  the  surface  blood-ves- 
sels contract,  and  the  blood  then  becomes  internally 
congested;  the  lungs  and  heart  may  be  affected,  and 
in  extreme  cases  death  results.  The  danger  of  freez- 
ing is  naturally  greatest  in  the  case  of  the  hands,  feet, 
ears,  and  nose,  which  are  most  exposed  and  can  least 
well  be  kept  warm.  The  skin  may  swell,  become 
thick  and  hard,  and  break  open.  The  power  of  re- 
sistance to  extreme  cold  depends  on  the  physical  con- 
dition, clothing,  food,  exercise,  exposure  to  sunshine, 
dampness,  wind,  and  other  factors.  The  feeling  of 
cold  is  increased  by  hunger,  and  rheumatic  people 
usually  suffer  most. 

The  physiological  effects  of  polar  cold  and  dark- 
ness have  been  fully  reported  upon  by  Arctic  and 
Antarctic  explorers.  The  recent  expeditions,  on 
which  very  careful  attention  has  been  given  to  pick- 
ing the  men,  as  well  as  to  their  health,  diet,  exercise, 
and  general  hygiene,  have  shown  much  less  marked 
effects  than  did  the  earlier  expeditions.  Among  the 
effects  which  have  often  been  observed  are  a  weaken- 
ing of  the  senses  of  taste  and  of  smell,  as  a  result  of 
congestion  and  over-secretion  on  the  mucous  mem- 
branes; depression,  apathy,  and  sleepiness,  often 


216  CLIMATE 

followed  by  nervous  excitement  and  even  in  some 
cases  by  insanity;  anaemia;  tendency  to  digestive  dis- 
orders and  dyspepsia;  constipation  or  diarrhoea; 
greatly  lessened  perspiration;  fading  of  hair  and 
beards;  change  of  colour  of  the  skin  to  pale  and  yel- 
low; a  lowering  of  the  body  temperature.  The  mo- 
notony of  the  polar  night  is  depressing  to  a  degree. 
Thirst  has  been  one  of  the  greatest  plagues  of 
Arctic  explorers  in  the  past.  The  result  of  a  large 
evaporation  from  the  lungs  into  the  dry,  cold  air, 
thirst  is  a  characteristic  of  the  deserts  of  snow  and 
ice  as  it  is  of  the  deserts  of  sand.  The  relief  of  this 
thirst  by  eating  snow  is  dangerous,  for  it  leads  to 
inflammation  of  the  throat  and  to  digestive  and  bowel 
troubles.  Moreover,  such  relief  is  but  temporary. 

It  has  been  pointed  out  by  physicians  that,  like 
the  polar  animals,  the  Eskimos  can  withstand  long 
periods  without  food;  that  their  intestinal  capacity 
is  increased  in  such  a  way  that  they  can  assimilate  a 
constant  meat  diet,  and  that  they  are  protected 
against  the  cold  by  thick,  fatty  tissues  and  by  their 
profuse  peripheral  circulation. 

Life  is  hard  in  the  polar  zones.  Deaths  by  drown- 
ing in  gales  at  sea,  by  freezing,  and  in  snowstorms 
are  frequent.  Yet,  on  the  other  hand,  most  of  the 
diseases  which  have  been  discussed  in  this  chapter  are 
rare  or  absent  in  the  far  north.  There  is  a  remark- 
able infrequency  of  infectious  diseases.  Polar  air  is 
very  free  from  micro-organisms — a  fact  which  is  due 
chiefly  to  lack  of  communication  with  other  parts  of 


THE  HYGIENE  OF  THE  ZONES  217 

the  world;  colds  are  reported  as  rare  or  unknown,  al- 
though changes  of  temperature  are  often  frequent 
and  large.  The  summer  sun,  both  by  direct  and  by 
reflected  radiation,  burns  and  bronzes  the  skin,  and 
may  cause  snow-blindness.  An  Arctic  summer,  with 
its  long  days,  crisp,  clean  air,  and  sunshine,  offers 
conditions  which  are  doubtless  excellent  for  many 
nervous  and  gastric  troubles,  and  one  may  predict  a 
considerable  development  of  summer  resorts  within 
the  Arctic  circle  for  the  pleasure-loving,  wealthy,  and 
unoccupied  persons  of  the  north  temperate  zone. 

Scurvy.  Scurvy  has  been  considered  a  polar  dis- 
ease par  excellence,  because  it  has,  in  the  past,  been 
prevalent  on  Arctic  expeditions,  and  is  found  to-day 
in  northern  latitudes.  Scurvy  is,  however,  known 
also  in  many  other  parts  of  the  world.  It  is  found 
under  conditions  of  overcrowding,  and  of  poor  ven- 
tilation, which  are  natural  consequences  of  extreme 
cold.  Cold  is  not  the  cause  of  the  disease,  for  scurvy 
is  found  in  warm  countries  also ;  but  rigorous  climatic 
conditions,  poor  food — especially  the  lack  of  fresh 
vegetables,  over-exertion,  depression,  lowered  vi- 
tality by  exposure  to  cold,  etc.,  are  predisposing 
causes.  The  best  preventives  of  scurvy  are  good 
food,  an  active  outdoor  life,  and  mental  stimulation. 
With  these  precautions  and  good  hygiene,  scurvy  has 
almost  disappeared  among  civilised  nations. 

Climate  and  Health:  General  Conchisions.  The 
old  view  concerning  the  paramount  influence  of  cli- 
mate upon  health  is  being  replaced  by  the  view  that 


218  CLIMATE 

good  hygiene  is  of  more  importance  than  climate 
alone.  Medical  science  has  done  much  to  stamp  out 
some  diseases  like  small-pox,  and  it  will  in  time  prob- 
ably largely  stamp  out  others,  like  malaria,  or  yellow 
fever,  or  even  tuberculosis  and  diphtheria.  Man 
himself,  not  climate,  is  being  held  responsible  for  the 
occurrence  of  this  or  that  disease  or  epidemic,  for  its 
distribution,  and  for  the  death-rates  resulting  from 
it.  Man  has  lowered  the  death-rate  from  disease 
most  wonderfully.  He  can  lower  it  still  further. 
Vaccination  for  small-pox ;  preventive  inoculation  for 
plague;  antitoxin  for  diphtheria;  good  food,  pure  air, 
and  exercise  for  scurvy;  draining  swamps  and  pools 
and  the  use  of  mosquito  netting  for  malaria;  pure 
water  for  cholera,  typhoid  fever,  and  dysentery— 
these  are  but  a  few  of  the  methods  now  employed  by 
man  in  his  war  against  disease. 

The  influence  of  climate  is  by  no  means  to  be  dis- 
carded as  of  no  account,  for  that  it  acts,  in  many 
ways,  both  directly  and  indirectly,  has  been  shown  in 
this  chapter.  The  newer  view  regarding  the  influence 
of  a  change  of  climate  as  a  preventive,  or  restorative. 
is  that  a  change  of  residence,  habits,  occupations,  food, 
is  usually  of  more  importance  than  the  change  in 
atmospheric  conditions.  If  pure  air,  good  food,  free- 
dom from  worry,  time  for  rest,  proper  exercise,  out- 
door life,  and  a  congenial  occupation  are  provided, 
many  bodily  and  mental  ailments  will  yield  to  the 
treatment.  Climate  is  to  be  considered,  because  it 
affects  our  bodily  comfort;  it  may  be  dull,  rainy,  and 


THE  HYGIENE  OF  THE   ZONES  219 

cheerless,  or  bright,  sunny,  and  exhilarating;  it  may 
tend  to  keep  us  indoors,  or  it  may  tempt  us 
to  go  out.  Thus  some  climates  will  naturally  be 
avoided,  and  others  sought  out,  and  the  choice  of  a 
suitable  climate  will  depend  upon  the  disease  to  be 
dealt  with.  As  a  recent  writer  has  well  said,  climate 
may  "  play  an  important  part  in  the  curative  process, 
but  the  climate  of  certain  localities  does  not  possess 
any  peculiar  properties  which  act  as  a  specific  on  cer- 
tain diseases." 


CHAPTER  VIII 

THE  LIFE  OF  MAN  IN  THE  TROPICS 

Climate  and  Man :  General— Some  Old  Views  Regarding  the  Effects 
of  Climate  on  Man — Factors  in  the  Problem  Offier  than  Cli- 
mate— Climate  and  Habitability — The  Development  of  the 
Tropics — The  Labour  Problem  in  the  Tropics — The  Govern- 
ment of  Tropical  Possessions — Primitive  Civilisation  and  the 
Tropics — Dwellings  in  the  Tropics — Clothing  in  the  Tropics — 
Food  in  the  Tropics — Agriculture,  Arts,  and  Industries  in  the 
Tropics — Some  Physiological  Effects  of  Tropical  Climates — 
The  Equatorial  Forests — The  Open  Grass-Lands  of  the 
Tropics:  Savannas — Trade  Wind  Belts  on  Land:  the  Deserts 
—Trade  Wind  Belts  at  Sea — Monsoon  Districts — Tropical 
Mountains. 

Climate  and  Man:  General.  Man's  climatic  en- 
vironment affects  him  in  many  ways.  His  clothing, 
dwellings,  food,  occupations,  and  customs;  his  physi- 
cal and  mental  characteristics;  his  systems  of  gov- 
ernment; his  migrations;  his  history — all  are  affected 
to  a  greater  or  less  degree. 

Civilised  man  protects  himself  more  or  less  suc- 
cessfully against  unfavourable  climatic  features. 
Thus,  there  is  a  gradual  transition  from  the  primitive 
shelter  made  of  branches  of  trees,  of  skins,  or  leaves, 
to  the  permanent  and  highly  elaborate  modern  build- 
ing, which  is  both  heated  and  cooled  artificially.  The 
building  materials;  the  methods  of  uniting  these  ma- 

220 


THE  LIFE  OF  MAN  IN  THE  TROPICS          221 

terials,  as  by  braiding,  or  binding,  or  by  the  use  of 
mortar,  usually  show  the  control  of  climate.  More- 
over, the  material  often  determines  the  general  plan 
of  the  building.  There  is  also  the  transition  from  the 
primitive  and  scanty  clothing  made  of  leaves  or  bark 
where  trees  grow,  or  the  skin  of  an  animal  where 
trees  are  lacking,  or  warmer  clothing  is  needed,  to  the 
manufactured  and  perhaps  imported  garment  of 
wool,  or  cotton,  or  silk.  Again,  there  is  the  increas- 
ing variety  of  food,  from  that  of  primitive  man,  sup- 
plied directly  where  he  lives,  to  the  highly  varied  diet 
found  in  a  civilised  community  to-day,  to  which  dis- 
tant latitudes  are  made  to  contribute  their  local 
delicacies. 

All  these  changes  man  has  brought  about.  But  he 
cannot  change  his  climate.  Slight  local  modifica- 
tions may  be  secured  here  and  there,  as  by  planting 
trees  to  serve  as  wind-breaks,  or  perhaps  by  in- 
creasing the  relative  humidity  a  little  through  the 
construction  of  an  artificial  reservoir.  No  such  modi- 
fication is  possible  in  man's  climatic  environment  as 
has  been  accomplished  on  the  surface  of  the  land  un- 
der human  agency.  The  atmosphere  is  as  essentially 
unalterable  as  it  is  all-pervading^  When  we  see  how 
plants  and  animals  are  affected  by  atmospheric  con- 
ditions, it  is  not  unreasonable  that  we  should  expect 
man  to  show  effects  of  a  similar  kind. 

Some  Old  Views  Regarding  the  Effects  of  Climate 
on  Man.  It  is,  however,  easy  to  go  too  far  in  calling 
upon  climate  to  explain  phenomena  which  we  may 


222  CLIMATE 

otherwise  find  it  difficult  to  account  for.  This  was 
the  mistake  formerly  made  by  many  writers  on  this 
subject,  as  has  been  clearly  pointed  out  by  Ratzel  in 
his  Anthropogeographie,  where  he  gives  an  outline 
of  many  of  these  earlier  views.  Maupertius  and 
others  held  that  the  colour  of  man's  skin  becomes 
paler  with  increasing  distance  from  the  equator. 
Livingstone  wTote  that  in  Africa  religious  ideas  also 
seemed  to  depend  on  distance  from  the  equator.  One 
writer  held  that  cold  produces  a  small  stature;  an- 
other believed  that  the  Pygmies  are  small  because  of 
the  heavy  seasonal  rains  which  fall  in  hot  equatorial 
Africa.  Climate  was  believed  to  explain  the  over- 
hanging eyebrows  and  partly-closed  eyes  of  the  ne- 
gro ;  the  small  eyes  and  beardless  faces  of  the  Chinese ; 
the  (supposed)  fact  that  more  twins  were  born  in 
Egypt  than  elsewhere.  And  so  on.  The  broad 
generalisations  of  Montesquieu,  Voltaire,  Buffon, 
Hume,  Buckle,  and  others,  furnish  interesting  read- 
ing, and  contain  much  that  is  suggestive  and  in- 
structive, but  they  usually  carry  us  well  beyond  the 
range  of  reasonable  probability.  Even  Hippoc- 
rates's  observations  on  climatic  controls  are  not 
without  value  to-day. 

Factors  in  the  Problem  Other  than  Climate.  To 
most  of  these  older  writers  climate  meant  more  than 
it  does  to-day.  It  included  much  of  what  is  now 
termed  our  whole  physical  environment.  Moreover 
they  based  their  conclusions  upon  incomplete  records, 
povering  far  too  short  periods  of  time.  It  must  be 


THE  LIFE  OF  MAN  IN  THE  TROPICS  223 

remembered  that  we  are  dealing  here  with  large, 
important,  highly  complex  phenomena.  Man  moves 
readily  from  place  to  place,  from  climate  to  climate. 
His  food,  drink,  habits,  occupations;  to  some  extent 
his  physical  and  mental  characteristics,  change  in 
consequence.  Inheritance,  intermarriage,  environ- 
ment, opportunities,  soil,  and  many  other  factors 
enter  in  to  determine  what  changes  individual  man  and 
the  race  as  a  whole  shall  undergo.  Time  is  a  very  im- 
portant element  in  the  final  result,  for  in  time  a 
gradual  adaptation  to  new  conditions  takes  place. 
Climate  is  but  one  of  many  controls,  albeit  a  most 
important  one,  for  it  largely  determines  what  many 
of  the  other  factors,  such  as  diet,  customs,  and  occupa- 
tions, for  example,  shall  be.  The  task  of  giving 
climate  its  proper  place  as  a  factor  controlling  the 
life  of  man  as  a  whole  is  a  difficult  one,  which  cannot 
be  definitely  and  satisfactorily  solved  to-day,  or 
to-morrow. 

It  would  take  us  far  beyond  the  limits  set  for  our\     . 
present  volume  were  we  to  attempt  any  consideration    \ 
of  the  many  complex  problems  in  connection  with  the     1 
possible  influences  of  climate  upon  the  physical  and 
mental  characteristics  of  man.     Investigations  along 
these  lines  have  given  rise  to  much  debate.     It  is  our 
present  purpose  merely  to  point  out  some  of  the  more 
simple  and  obvious  ways  in  which  the  life  of  man  is 
controlled  by  climate.     This  control,  it  should  be  ob-     I 
served,  is  either  direct,  where  physical  and  mental 
changes  under  climatic  stimulus  are  concerned,  or 


224  CLIMATE 


indirect,  as  when  climate  acts  upon  man  through  its 
influence  over  the  distribution  of  the  animals  and 
plants  upon  which  man  depends  for  his  food,  cloth- 
ng,  and  materials  of  various  kinds. 
\Climate  and  Habitability.  Climate  determines 
both  how  and  where  man  shall  live.  It  classifies  the 
earth's  surface  for  us  into  the  so-called  habitable  and 
uninhabitable  regions.  The  deserts  of  sand  and  the 
deserts  of  snow  and  ice,  whether  the  latter  be  near  sea- 
level  or  high  up  on  mountain  tops,  are  alike  climatic, 
the  former  because  of  aridity;  the  latter  because  of 
cold.  The  only  non-climatic  deserts  are  recent  lava- 
flows.  Where  a  soil  is  present  which  is  not  frozen 
for  much  over  half  the  year,  and  where  there  is 
reasonable  temperature  and  sufficient  rainfall,  plants 
and  animals  are  found,  ranging  from  few  and  lowly 
forms  where  conditions  are  the  hardest  and  where 
all  organic  life  is  especially  adapted  to  these  condi- 
tions, to  the  greatest  abundance  where  conditions  are 
most  favourable. 

Man  is  influenced  by  much  the  same  controls  as 
those  which  affect  plants  and  the  lower  animals. 
From  the  highest  latitudes  he  is  excluded  by  cold. 
The  higher  altitudes  are  hostile  both  because  of  cold 
and  of  diminished  pressure.  The  deserts  of  sand  are 
uninhabited,  or  thinly  populated,  by  reason  of  aridity. 
Forests,  where  rainfall  is  abundant,  are  unfavourable 
to  a  dense  population.  The  trees  must  be  cleared 
away  before  settlement  is  easy.  Man  is  widely  dis- 
tributed over  the  earth's  surface.  In  his  migrations 


THE  LIFE  OF  MAN  IN  THE  TROPICS  225 

he  has  carried  with  him,  beyond  their  original  limits, 
many  plants  and  animals.  Ratzel  points  out  that 
the  coldest  place  in  the  world  in  January  is  a  large 
Siberian  city,  Verkhoyansk,  while  one  of  the  hottest 
places  in  the  world  is  Massowa,  on  the  Red  Sea,  the 
capital  of  the  Italian  colony  of  Eritrea.  But  the  life 
of  man  is  harder  here  and  easier  there,  according  to 
climatic  conditions  and  the  scarcity  or  abundance  of 
plant  and  animal  life. 

Man  is  distributed  in  great  belts  around  the  world, 
corresponding  roughly  to  the  broad  zones  of  vege- 
tation, desert,  steppe,  and  forest,  the  limits  of  which 
are  set  by  temperature  and  rainfall,  but  man  is  much 
more  dependent  on  rainfall  than  ugon_  tem^eratore^: 
Water  he  must  have,  directly  from  the  clouds,  or  in- 
directly through  rivers,  or  springs,  or  wells,  or  from 
melted  snow  and  ice.  There  are  certain  common 
conditions  of  life  which  affect  the  people  who  live  in 
the  same  zone  in  the  same  broad,  general  way,  just  as 
these  zones  have  similar  general  conditions  of  winds 
and  of  rainfall.  This,  as  Ratzel  has  pointed  out, 
means  that  there  is  a  climatic  factor  at  work  to  main- 
tain differences  between  the  people  of  different  zones, 
in  spite  of  the  great  movements  which  are  constantly 
tending  to  produce  uniformity.  Obviously,  the  dif- 
ferences in  the  life  of  man  which  depend  upon  climate 
will  be  most  noticeable,  and  will  be  likely  to  have  the 
greatest  historical  significance,  when  marked  differ- 
ences of  climate  are  found  close  together,  as  in  the 
case  of  mountain  ranges  like  the  Alps,  or  of  a  pro- 


226  CLIMATE 

j  nounced  lowland,  plateau,  and  mountain  topography 
like  that  of  Peru  or  Mexico. 

All  the  regions  of  sparse  population  are  gradu- 
ally being  encroached  upon  by  an  invasion  from  their 
borders.  Forests  are  being  cleared  and  replaced  by 
open  agricultural  lands.  Wheat  and  corn  are  re- 
placing grass  on  the  steppes  and  savannas,  especially 
where  irrigation  can  be  practised.  Deserts  are  being 
reclaimed  for  farming  here  and  there  where  water 
is  available.  The  more  civilised  man  becomes,  the 
denser  the  population  which  the  different  parts  of  the 
earth  can  be  made  to  support.  From  the  wandering 
hunting  and  fishing  tribes  of  the  African  forest  or  of 
the  borders  of  the  Arctic  sea,  through  the  farming 
populations  of  the  cleared  forest  and  of  the  steppe, 
to  the  crowded  industrial  centres  of  the  modern  city, 
there  is  such  a  gradation.  It  is  the  story  of  a  more 
complete  to  a  less  complete  mastery  of  man  by  his 
environment.  But  in  spite  of  all  that  man  can  do, 
the  larger  climatic  limitations  persist.  The  Green- 
land desert  of  snow  and  ice,  and  the  Saharan  desert  of 
sand,  must  remain  practically  deserted. 

The  Development  of  the  Tropics.  Within  the 
tropics,  under  the  equatorial  sun,  and  where  there  is 
abundance  of  moisture,  animal  and  plant  life  reach 
their  fullest  development.  Here  are  the  lands  which 
are  most  valuable  to  the  white  man  because  of  the 
wealth  of  their  tropical  products.  Here  are  the 
tropical  "  spheres  of  influence  "  or  "  colonies  "  which 
are  among  his  most  coveted  possessions.  It  is  in  this 


THE  LIFE  OF  MAN  IN  THE  TROPICS  227 

belt  that  food  is  provided  for  man  throughout  the 
year  without  labour  on  his  part;  in  which  frost  and 
drought  need  not  be  feared;  where  shelter  and  cloth- 
ing are  so  easily  provided,  and  often  so  unnecessary, 
that  life  becomes  too  easy.  Nature  does  too  much; 
there  is  little  left  for  man  to  do.  The  simplicity  of 
life,  so  far  as  providing  food  is  concerned,  has  been 
emphasised  by  many  writers.  We  are  told  that  three 
bread-fruit  trees  furnish  enough  food  for  one  man; 
that  a  labourer  needs  only  twelve  bananas  for  his 
daily  food;  that  one  day  a  week  is  enough  time  to 
spend  in  caring  for  a  manioc  plantation;  that  two 
days'  work  a  week  is  often  enough  to  enable  a  man  to 
support  a  family;  that  a  month's  labour  will  provide 
for  a  Malay  more  sago  than  he  can  use  in  a  year,  etc. 
Stories  are  told  of  shipwrecked  seamen  in  the  tropi- 
cal Pacific  who  lived  for  many  days  on  one  cocoanut 
a  day  for  each  man.  Captain  Cook  put  the  case  very 
emphatically  when  he  said  that  a  South  Sea  Islander 
who  plants  ten  bread-fruit  trees  does  as  much  to- 
wards providing  food  for  his  family  as  does  a  man  in 
northern  Europe  who  works  throughout  the  year. 

In  a  debilitating  and  enervating  climate,  without 
the  necessity  of  work,  the  will  to  develop  both  the 
man  who  inhabits  the  tropics,  and  also  the  resources 
of  the  tropics,  is  generally  lacking.  Voluntary  pro- 
gress toward  a  higher  civilisation  is  not  reasonably 
to  be  expected.  The  tropics  must  be  developed  un- 
der other  auspices  than  their  own.  '  Where  nature 
lavishes  food  and  winks  at  the  neglect  of  clothing  and 


228  CLIMATE 

shelter,  there  ignorance,  superstition,  physical  prow- 
ess, and  sexual  passion  have  an  equal  chance  with 
intelligence,  foresight,  thought,  and  self-control."  l 

There  is  no  superfluous  energy  for  the  higher 
things  of  life.  Thus  it  has  come  about  that  the  na- 
tives of  the  tropics  have  the  general  reputation  of 
being  indolent  and  untrustworthy;  of  always  being 
ready  to  put  off  until  "  to-morrow."  Obviously,  no 
such  sweeping  generalisation  is  to  be  taken  too  liter- 
ally, for  the  lower  latitudes  have  produced  many  men 
far  from  deficient  in  physical  and  intellectual  power. 
Moreover  in  those  parts  of  the  tropics  where  natural 
conditions  are  more  severe,  the  natives  are  usually 
more  industrious.  But  it  is  true  that  the  energetic 
and  enterprising  races  of  the  world  have  not  devel- 
oped under  the  easy  conditions  of  life  in  the  tropics. 
As  Edward  Whymper's  Swiss  guide  said  of  the  na- 
tives of  Ecuador,  "  it  would  be  good  for  tropical 
peoples  to  have  a  winter."  Guyot  has  put  the  case  in 
this  way: 

A  nature  too  rich,  too  prodigal  of  her  gifts,  does  not 
compel  man  to  snatch  from  her  his  daily  bread  by  his  daily 
toil.  A  regular  climate,  the  absence  of  a  dormant  season, 
render  forethought  of  little  use  to  him.  Nothing  invites  him 
to  that  struggle  of  intelligence  against  nature  which  raises 
the  forces  of  man  to  so  high  a  pitch,  but  which  would  seem 
here  to  be  hopeless.  Thus  he  never  dreams  of  resisting  this 
all-powerful  physical  nature ;  he  is  conquered  by  her ;  he  sub- 
mits to  the  yoke,  and  becomes  again  the  animal  man, — for- 
getful of  his  high  moral  destination. 

The  movements  of  the  body,  the  habit  of  carrying 

iJohn  R.  Commons,  The  Chautauquan,  May,  1904,  p.  222. 


THE  LIFE  OF  MAN  IN  THE  TROPICS         229 

loads  on  the  head,  even  the  native  dances,  have  been 
thought  by  some  to  show  the  enervating  effects  of  the 
climate.  One  writer  has  even  gone  so  far  as  to  see 
similar  effects  in  the  domestic  animals,  which  he  be- 
lieves to  be  more  docile  than  those  in  extra-tropical 
latitudes. 

The  Labour  Problem  in  the  Tropics.  "  What 
possible  means  are  there  of  inducing  the  inhabitants 
of  the  tropics  to  undertake  steady  and  continuous 
work,  if  local  conditions  are  such  that  from  the  mere 
bounty  of  nature  all  the  ambitions  of  the  people  can 
be  gratified  without  any  considerable  amount  of 
labour?  "  In  these  words,  Alleyne  Ireland  well  sums 
up  the  labour  problem  in  the  tropics.  If  the  natives 
are,  on  the  whole,  disinclined  to  work  of  their  own 
accord,  then  either  forced  native  labour,  which  is  con- 
trary to  the  spirit  of  the  times,  or  imported  inden- 
tured labour,  becomes  inevitable  if  the  tropics  are  to 
be  developed.  With  few  exceptions,  and  those  where 
the  pressure  of  a  large  population  necessitates  labour, 
effective  development  has  been  accomplished  only 
where  imported  Chinese,  Japanese,  or  coolie  labour 
has  been  employed,  under  some  form  of  contract. 
Negro  slavery  began  in  the  West  Indies,  under  early 
Spanish  rule,  and  its  perpetuation  was  certainly  in 
part  aided  by  climatic  controls.  The  best  develop- 
ment of  many  tropical  lands  depends  to-day  upon 
Chinese  labour.  It  will  be  so  in  the  Philippines.  In 
Java,  Holland  has  succeeded  by  forcing  the  natives 
to  work. 


230  CLIMATE 

With  a  large  native  class  which  is  indolent,  work- 
ing intermittently  for  low  wages,  or  which  is  bound 
under  some  form  of  contract,  it  follows  that  the  na- 
tive or  imported  labouring  classes  are  separated  by  a 
broad  gulf  from  the  upper,  employing  class,  which  is 
usually  essentially  foreign  and  white.  The  latter 
class  tends  to  become  despotic;  the  former,  to  become 
servile.  Marked  social  inequalities  thus  result,  ac- 
centuated by  the  fact  that  the  foreign-born  white  is 
usually  debarred  from  all  hard  labour  in  a  hot  tropi- 
cal climate.  White  labourers  are  not  likely  to  be- 
come dominant  in  the  tropics  for  two  reasons : — first, 
because  the  climate  is  against  them;  and  second,  be- 
cause the  native  is  already  there,  and  his  labour  is 
cheaper.  White  men  are  not  doing  the  hard  daily 
labour  of  India,  or  of  Java,  or  of  the  Philippines,  or 
even  of  Hawaii.  They  are  directing  it. 

The  Government  of  Tropical  Possessions.  The 
government  of  European  possessions  in  the  tropics 
has  thus  far  been  determined  chiefly  by  three  con- 
siderations: (1)  The  general  incapacity  of  the  na- 
tives, through  ignorance,  or  lack  of  interest,  or 
their  undeveloped  condition,  to  govern  them- 
selves properly.  (2)  The  fact  that  the  white  resi- 
dents are  generally  comparatively  few  in  number  and 
are  only  temporarily  in  the  country,  to  make  money 
and  then  to  go  home  again.  The  white  population 
is  often  composed  chiefly  of  men — soldiers,  officials, 
merchants,  adventurers.  There  is  little  inducement 
to  found  permanent  homes.  (3)  The  marked  class 


THE  LIFE  OF  MAN  IN  THE  TROPICS  231 

distinctions  already  referred  to.  These  generalisa- 
tions must  obviously  not  be  carried  too  far. 
Hawaii,  very  favourably  situated  as  regards  climate, 
will  in  time  become  an  American  State,  and  Brazil, 
most  of  whose  immense  area  is  typically  tropical,  has 
an  increasing  European  immigration  of  permanent 
settlers.  But  what  has  been  said  is,  in  the  main,  true. 
The  white  residents  constitute  a  caste,  and  naturally 
become  the  rulers,  the  home  government  retaining 
general  control,  often  by  force  of  arms.  The  native 
population,  although  largely  in  the  majority,  may 
have  little  or  no  voice  in  its  own  government.  This 
is  clearly  not  a  democracy.  It  thus  comes  about  that 
the  tropics  are  governed  largely  from  the  temperate 
zone;  the  standards,  ideals,  motives,  come  from  an- 
other land.  And  where  governed  under  their  own 
auspices,  as  independent  republics,  the  success  has  not 
been  great.  Buckle  first  strongly  emphasised  the 
point  that  hot  countries  are  conducive  to  despot- 
ism and  cold  countries  to  freedom  and  independence; 
and  James  Bryce  has  recently  clearly  set  forth  the 
climatic  control  of  government  in  an  essay  on  "  Brit- 
ish Experience  in  the  Government  of  Colonies " 
(Century,  March,  1899,  718-729).  The  very  Euro- 
peans who  exercise  the  controlling  power  in  the  trop- 
ics,^themselves  tend  to  become  enervated  if  they  live 
there  long;  they  lose  many  of  the  standards  and 
ideals  with  which  they  started;  they  not  uncommonly 
tend  to  fall  towards  the  level  of  the  natives  rather 
than  to  raise  the  standards  of  the  latter.  The  pecu- 


232  CLIMATE 

liar  situation  which  may  arise  from  the  government 
of  a  tropical  possession  in  which  the  white  race  does 
not  become  acclimated  has  been  emphasised  by  Dr. 
Goldwin  Smith  in  a  recent  discussion  of  British  rule 
in  India.  "  British  Empire  in  India,"  he  says,  "  is  in 
no  danger  of  being  brought  to  an  end  by  a  Russian 
invasion.  It  does  not  seem  to  be  in  much  danger  of 
being  brought  to  an  end  by  internal  rebellion.  Yet 
it  must  end.  Such  is  the  decree  of  nature.  In  that 
climate  British  children  cannot  be  reared.  No  race 
can  forever  hold  and  rule  a  land  in  which  it  cannot 
rear  its  children."  The  future  of  tropical  possessions 
and  "  spheres  of  influence  "  offers  many  problems  of 
great  complexity,  the  solution  of  which  is  largely  con- 
trolled by  the  factor  of  climate. 

Primitive  Civilisation  and  the  Tropics.  There  are 
reasons  for  thinking  that  primitive,  pre-historic  man, 
in  his  earliest  stages,  when  most  helpless,  was  an  in- 
habitant of  the  tropics;  that  he  lived  under  the  mild, 
uniform,  genial  climate  of  that  zone,  where  food  was 
easily  obtained  and  protection  against  the  inclemen- 
cies of  the  weather  least  necessary.  There  has  been 
a  belief  that  southern  Asia,  bordering  on  the  Indian 
Ocean,  with  its  numerous  bays,  was  probably  the 
cradle  of  humanity.  Civilised  man  is  believed  by 
many  to  have  appeared  first  on  the  delta  formed  at 
the  head  of  the  Persian  Gulf  by  the  Tigris  and  Eu- 
phrates rivers,  where  also  wheat  was  very  likely  first 
grown.  Ancient  civilisations  seem  to  have  developed 
in  the  drier  portions  of  the  tropics,  where  irrigation 


THE  LIFE  OF  MAN  IN  THE  TROPICS  233 

was  necessary  in  order  to  insure  abundant  and  regu- 
lar crops,  and  where  lived  races  more  energetic  and 
more  hardy  than  those  of  the  damper  and  rainier  por- 
tions of  the  tropics,  with  more  luxuriant  vegetation. 
As  Professor  Hilgard  *  has  well  said : 

It  is  hardly  doubtful  that  the  ancient  *  Kulturvolker  * 
recognised  these  advantages  (of  irrigated  lands)  by  experi- 
ence, and  eschewed  the  laborious  task  of  rendering  cultivable 
the  comparatively  infertile,  or,  at  least,  readily  exhausted, 
lands  of  the  forest  regions.  .  .  .  And  it  is  also  clear  that, 
inasmuch  as  the  establishment  and  maintenance  of  irrigation 
canals  necessarily  involve  cooperation,  and  therefore  a  rather 
high  degree  of  social  organisation,  the  conditions  of  the  arid 
regions  were  exceptionally  conducive  to  the  establishment  of 
the  highly  complex  polities  of  which  the  vestiges  are  now  be- 
ing unearthed  in  what  we  are  in  the  habit  of  calling  deserts. 

Civilisation  was  thus  probably  first  developed, 
not  where  the  overwhelming  superabundance  of 
nature's  gifts  seems  to  offer  the  best  conditions, 
but  where  man  was  under  some  stress  of  labour, 
some  spur  to  effort,  in  less  favourable  natural 
conditions,  but  such  as  developed  him.  Within 
the  tropics,  the  greatest  progress  later  came,  not  on 
the  damp  lowlands,  but  on  the  less  fertile  plateaus  of 
Mexico  and  of  Peru,  where  the  Aztecs  and  Incas 
made  their  marvellous  progress  in  the  drier,  cooler, 
and  more  rigorous  climates  of  altitudes  over  7000  or 
8000  feet  above  sea-level.  Ratzel  has  pointed  out, 

1  E.  W.  Hilgard :  "  The  Causes  of  the  Development  of  Ancient 
Civilisations  in  Arid  Countries,"  No.  Amer.  Rev.,  vol.  175,  1902, 
p.  314. 


234  CLIMATE 

in  the  case  of  the  ruins  found  on  the  lowlands  of 
Yucatan  and  of  farther  India,  that  when  such  build- 
ing operations  are  carried  through  by  the  autocratic 
rule  over  a  subject  class,  the  situation  is  very  different 
from  that  in  which  we  see  spontaneous  action  on  the 
part  of  a  whole  people. 

The  nations  living  in  ease  on  the  tropical  lowlands 
were  naturally,  from  early  days,  the  object  of  fre- 
quent attacks  and  invasions  at  the  hands  of  the  more 
active  and  more  warlike  races  living  in  more  rigorous 
climates  farther  north,  or  at  greater  altitudes  on 
mountains  or  plateaus.  The  invading  tribes,  having 
in  time  become  enervated  by  an  easy  existence  on  the 
warm  lowlands,  have  themselves  often  been  later 
overcome  by  a  new  enemy  from  the  north.  Some  of 
the  greatest  migratory  movements  in  history  have 
taken  place  from  colder  to  warmer  climates,  as  part 
of  this  general  equatorward  tendency  in  both  tem- 
perate and  tropical  zones.  The  barbarous  tribes 
broke  through  the  northern  passes  and  descended  onto 
the  more  genial  and  more  fruitful  lowlands  of  India, 
being  helped  to  do  this  by  the  ease  of  the  descent. 
Such  mountain  systems  as  the  Himalayas,  or  the 
Alps,  stretching  east  and  west,  are  natural  climatic 
divides  between  more  genial  and  more  severe  cli- 
mates, and  have  often  been  crossed  by  invading  arm- 
ies from  the  north.  The  descent  of  the  Aryans  into 
India;  the  Manchurian  conquest  of  China;  the  in- 
vasions of  Greece  and  Italy  from  the  north;  the 
southward  movement  of  Toltecs  and  Aztecs  in  Mex- 


THE  LIFE  OF  MAN  IN  THE  TROPICS  235 

ico,  have  been  cited  as  illustrations  of  this  equator- 
ward  tendency.  In  the  southern  hemisphere,  it  has 
been  suggested  that  the  Kaffirs  have  shown  the  same 
tendency — there  northward, — as  did  the  native  Pata- 
gonians  in  their  predatory  expeditions  to  the  north. 
The  equatorward  tendency  may  be  seen  to-day  in 
the  extension  of  European  "  spheres  of  influence," 
especially  in  Africa,  the  object  now  being  essentially 
a  mercenary  one,  and  not  a  seeking  for  new  homes  in 
a  more  genial  climate. 

Dwellings  in  the  Tropics.  Dwellings,  clothing, 
and  food  are  easily  provided  in  the  hot  climates  of 
the  moist  tropics.  In  the  deserts  and  on  the  moun- 
tains the  conditions  of  life  are  harder.  The  protec- 
tion that  is  needed  against  sun  and  rain,  and  the 
lowered  temperatures  of  the  tropical  night,  is  usually 
very  simple.  Man  spends  most  of  his  life  outdoors. 
The  building  materials  are  ready  at  hand  and  simple. 
Many  of  the  primitive  native  huts  are  loosely  made 
of  bamboo  or  other  pliable  trees,  where  such  are 
available  (e.  g.,  the  mimosa  used  by  the  Hottentots)  ; 
of  palm  and  coeoanut  leaves,  sugar-cane,  or  grass. 
Pointed  roofs,  supported  on  poles,  and  wooden 
frames  with  mats  for  walls,  are  a  characteristic  style 
of  architecture.  In  some  places  temporary  huts  are 
made  of  skins,  while  more  permanent  dwellings  are 
better  built,  with  good  roofs.  The  permanent  dwell- 
ings in  tropical  cities  are  oftenest  built  of  stone,  with 
thick  walls.  The  old  Spanish  and  Portuguese  idea 
was  also  to  have  narrow  streets,  in  order  that  the  sun- 


236  CLIMATE 

light  might  be  shut  out  as  much  as  possible.  In  the 
newer  portions  of  tropical  cities,  however,  wide 
streets  and  fine  boulevards  are  being  laid  out.  In 
the  modern  houses  built  for  European  residents  in 
the  tropics,  the  rooms  are  large,  airy,  and  well  venti- 
lated; there  is  a  minimum  of  furnishings;  there  are 
broad  verandas  with  screens  for  protection  against 
the  sun;  there  is  a  proper  air  space  between  roof  and 
ceiling.  Stoves  and  fireplaces  for  heating  purposes 
are  unnecessary,  and  the  absence  of  chimneys  on  the 
tops  of  city  houses  has  often  attracted  the  attention 
of  newcomers  from  colder  latitudes.  Nevertheless, 
in  some  places  the  natives  are  so  sensitive  to  the 
nocturnal  cooling  that  they  keep  themselves  warm  by 
fires  at  night.  Much  difficulty  is  experienced  on 
account  of  the  destructive  action  of  ants  and  other 
insects,  and  of  the  dampness,  as  well  as  of  sudden 
tropical  rains  and  floods.  Even  in  dry  climates, 
buildings  do  not  last  well,  unless  built  of  stone.  As 
the  prevailing  winds  are  easterly,  the  eastern  quarters 
of  the  cities  are  usually  the  more  desirable  and  the 
more  fashionable,  and  are  therefore  inhabited  by  the 
wealthier  classes.  It  is  the  habit  of  those  who  live 
in  the  tropics  to  stop  work  and  stay  indoors  during 
the  hottest  part  of  the  day.  Business  is  done  in 
morning,  or  later  afternoon,  and  the  afternoon  siesta 
has  become  a  characteristic  of  the  people.  The  late 
afternoon  is  the  time  for  the  fashionable  outdoor  life 
in  the  park,  on  the  promenade,  or  at  the  club. 


THE  LIFE  OF  MAN  IN  THE  TROPICS  237 

Clothing  in  the  Tropics.  The  clothing  of  the  na- 
tives of  the  tropics  is  of  the  simplest  kind,  often  so 
scanty  as  hardly  to  be  called  clothing  at  all. 
In  the  moister  portions  it  not  infrequently  consists 
solely  of  aprons  made  of  grass,  leaves,  bark,  or 
reeds.  The  children  generally  go  naked.  Where 
the  diurnal  temperature  changes  are  marked,  heavier 
clothing  is  usually  worn  at  night.  The  clothing  of 
Europeans  and  Americans  is  loose  and  light  in  colour 
and  weight,  but  thin  woollens  are  by  no  means  to  be 
discarded  altogether,  for  they  are  useful  during  the 
cooler  evening  hours.  Light  headgear,  for  protec- 
tion against  the  sun,  such  as  wide-brimmed  straw 
hats  or  pith  helmets,  sun  umbrellas,  and  low  shoes 
are  used.  Great  care  has  been  taken  to  devise  the 
most  suitable  uniform  for  white  troops  in  the  tropics, 
even  down  to  the  most  minute  details  of  equipment. 
The  kind  of  material,  the  number  and  cut  of  the  dif- 
ferent garments,  even  the  best  kind  of  belt  and 
shoulder-straps,  have  received  attention.  Campaign- 
ing in  the  tropics  is  very  different  from  ordinary  ser- 
vice in  the  temperate  zones,  and  all  these  details  need 
care.  It  is  the  general  opinion  that  a  loose, 
light  uniform,  of  porous  material,  with  a  minimum  of 
straps,  belts,  and  pouches,  is  the  best.  As  to  ma- 
terials, khaki  has  come  into  extensive  use  and  is  very 
popular.  "  Keep  the  head  cool  and  the  abdomen 
warm"  is  the  best  rule  for  white  residents  of  the 
tropics  to  follow. 


238  CLIMATE 

Food  in  the  Tropics.  Fruits,  especially  the  ba- 
nana, cocoanut,  and  bread-fruit,  and  rice,  manioc, 
yams,  sago,  and  sugar-cane  are  staple  articles  of  food. 
Meat  and  fish  are  not  much  used.  In  the  deserts  the 
date-palm  is  an  important  article  of  food,  and  where 
irrigation  is  practised  a  variety  of  cereals  and  fruits 
is  usually  grown.  Of  late  years,  much  attention  has 
been  paid  by  military  officials  to  the  question  of  the 
best  ration  for  white  troops  who  serve  in  the  tropics. 
The  general  feeling  is  that  a  light  diet  consisting 
chiefly  of  fruit,  vegetables,  and  cereals,  with  a  mini- 
mum of  nitrogenous,  heat-producing  foods5  is  the 
most  likely  to  keep  the  men  in  good  health.  A  light 
midday  meal  is  recommended.  There  are,  however, 
those  who  hold  that  the  prevailing  anaemic  condition 
of  the  tropical  natives  is  largely  due  to  the  deficiency 
of  meat  in  their  diet,  and  who  therefore  urge  that 
meat  should  be  eaten  in  reasonable  quantity. 

There  is  much  difficulty  in  preserving  perishable 
food-products.  Such  articles  sent  from  cooler  lati- 
tudes for  use  in,  or  for  transportation  across,  the 
tropics,  need  special  protection,  by  refrigeration  or 
quick  carriage.  The  increase  .of  transportation  by 
steam  in  place  of  sail,  and  the  opening  of  the  Suez 
Canal,  have  both  been  factors  of  importance  in  meet- 
ing this  difficulty.  It  is  distinctly  an  advantage  for 
a  country  to  sell  its  food  products  to  other  countries 
on  its  own  side  of  the  equator.  Frozen  meat, 
carried  long  distances  by  sea  across  the  tropics,  is 
not  as  good  as  fresh  meat,  and  is  also  poorer  than 


TEE  LIFE  OF  MAN  IN  THE  TROPICS  239 

meat  carried  at  sufficiently  low  temperatures  to  pre- 
serve, without  actually  freezing  it.  The  need  for 
preserving  perishable  food  has  led  to  an  increasing 
demand  for  ice,  and  hence  to  the  multiplication  of 
artificial-ice  plants.  Recently  there  comes  a  demand 
from  one  tropical  country  (India)  for  refrigerator 
cars  for  the  transportation  of  milk. 

Agriculture,  Arts,  and  Industries  in  the  Tropics. 
The  need  of  labour  in  order  to  procure  a  good  return 
from  the  ground  is  so  slight  that  agriculture  has  not 
yet  made  much  progress  in  the  tropics  as  a  whole. 
Where  frost  need  riot  be  feared,  where  crops  ripen  all 
the  year  around,  and  where  the  soil  is  rich  with  de- 
caying vegetable  matter,  agriculture  is  naturally 
slow  to  improve.  Yet  there  are  native  peoples  who 
have  advanced  much  farther  than  might  be  expected, 
as  is  seen,  for  example,  in  the  cultivation  of  rice  in 
the  Malay  archipelago  and  in  farther  India;  in  the 
state  of  Polynesian  agriculture;  in  the  success  at 
farming  attained  by  many  negroes  in  Africa.  Tropi- 
cal soils  are  by  no  means  all  as  fertile  as  is  generally 
believed.  The  warm  rains  throughout  the  year 
leach  out  the  soil,  carrying  off  many  salts  and 
leaving  the  land  poor ;  the  laterite  soils  which  are  com- 
mon in  the  tropics  are  very  poor  in  plant-food 
ingredients. 

There  have  thus  far  been  comparatively  few  native 
industries  in  the  tropics,  for  the  reason,  doubtless, 
that  the  necessities  of  life  are  readily  supplied  with- 
out the  need  of  manufacture.  In  the  future,  with 


240  CLIMATE 

increasing  exploitation  by  the  white  race,  and  under 
the  control  of  it,  and  with  growing  demands  on  the 
part  of  the  natives  themselves,  tropical  industries  are 
certain  to  develop.  Yet  many  tropical  natives  show 
great  ingenuity  in  the  use  and  adaptation  of  the 
simple  natural  products  to  which  they  have  access. 
Thus  the  shell  of  the  cocoanut  is  made  into  bowls  and 
other  utensils;  the  cocoanut  fibres  are  plaited  into 
thatch,  baskets,  and  mats;  the  cocoanut  stems  are 
used  in  the  building  of  houses  and  boats.  Grass 
and  reeds  are  plaited,  and  the  bark-cloth  of  the  Pa- 
cific islanders  and  of  central  Africa  is  so  widely  used, 
and  serves  its  purposes  so  well,  that  it  has  very  prob- 
ably kept  the  natives  who  use  it  from  advancing  to 
weaving  and  spinning.  Bamboo  and  rattan  are 
widely  used  for  domestic  utensils  of  all  sorts;  for 
hunting  and  agricultural  implements;  in  construct- 
ing houses,  boats,  rafts,  and  vehicles  for  transporta- 
tion; in  making  pipes  and  musical  instruments;  and 
for  other  purposes;  even  for  food,  rope,  and  string. 
From  the  tropics  man  procures  many  things  in  ad- 
dition to  the  plant  products.  For  example,  the 
warm  tropical  oceans  yield  him  pearls  and  corals.  It 
is  an  interesting  fact  that,  at  the  present  time,  Euro- 
pean countries,  particularly  Germany,  are  devising 
and  manufacturing  machines  especially  intended  for 
harvesting  and  preparing  for  export  the  products  of 
the  tropics,  such  as  machines  for  splitting  cocoanuts; 
for  preparing  and  extracting  oil  from  the  palm  fruit ; 
for  making  caoutchouc  from  the  sap  of  the  rubber 


THE  LIFE  OF  MAN  IN  THE  TROPICS  241 

tree,  etc.  Germany  is  also  devising  plans  for  tropi- 
cal cultivators,  railroads,  and  houses. 

Special  precautions  are  necessary  in  packing  many 
manufactured  goods  that  are  to  be  transported 
across  the  equator,  in  order  to  protect  them  from  in- 
jury by  the  dampness.  Leather  goods,  textiles,  and 
paper  are  liable  to  be  stained.  Arms,  cutlery,  and  all 
metal  goods  need  the  utmost  care  to  keep  them  from 
rusting.  These  are  best  preserved  when  packed  in 
cases  lined  with  some  absorbent  wood  well  saturated 
with  hot  paraffine  wax.  It  has  recently  been  pointed 
out  in  a  Vienna  trade  journal,  that  the  preservation 
of  lacquered  shoes  sent  from  Europe  to  Australia 
depends  upon  the  circumstance  whether  they  may  be 
kept  moderately  cool  by  the  ocean  water,  low  down 
in  the  ship's  hold,  or  are  near  the  deck,  exposed  to  the 
heat.  In  Indian  warehouses  woven  goods  are  affected 
by  the  dampness  in  such  a  way  that  they  have  different 
lengths,  although  all  uniformly  woven.  Even  in  the 
dry  month  of  February,  at  Bombay,  closely  woven 
imported  calicoes,  exposed  to  the  air,  experience 
changes  in  length  from  day  to  day  amounting  to  3 
per  cent.  Ordinary  salt  absorbs  so  much  moisture 
in  the  damp  latitudes  that  it  has  been  necessary  to 
prepare  a  salt  which  shall  escape  this  difficulty. 

Some  Physiological  Effects  of  Tropical  Climates. 
We  are  not  here  concerned  with  the  many  complex 
questions,  physiological  and  ethnological,  which  have 
arisen  in  connection  with  the  effects  of  tropical  cli- 
mates upon  man.  There  has  been  much  debate  con- 

16 


242 


CLIMATE 


earning  the  effect  of  the  climate  upon  the  colour  of 
the  skin.  It  was  natural  that  many  early  writers 
should  see  in  the  black  skin  of  the  negro  an  effect  of 
the  tropical  sun,  and  should  explain  the  paler  colours, 
and  white,  as  resulting  from  residence  in  higher  lati- 
tudes. It  was  pointed  out,  e.  g.f  that  among  certain 
tropical  natives  the  women,  who  live  indoors,  are 
lighter  in  colour  than  the  men,  who  are  more  ex- 
posed. It  may  be  remembered  that  Darwin,  in  his 
Descent  of  Man,  pointed  out  that  the  distribution  of 
coloured  races  does  not  coincide  with  corresponding 
differences  of  climate,  and  that  no  change  in  colour 
has  taken  place  in  the  Dutch  who  have  lived  for  sev- 
eral generations  in  south  Africa.  Darwin  also 
thought  it  not  an  improbable  conjecture  that  the  im- 
munity of  negroes  from  certain  diseases  might  be 
correlated  with  the  colour  of  their  skins,  and  that  this 
colour  might  have  been  acquired  because  darker  in- 
dividuals escaped  during  successive  generations  from 
these  diseases.  However  opinions  may  differ  con- 
cerning the  origin  of  the  black  skin  of  the  negro,  it  is 
clear  that  this  colour  is  an  advantage,  rather  than 
otherwise,  in  helping  to  cool  the  body  through  profuse 
perspiration  and  the  resulting  evaporation.  Black 
skin,  however  it  may  have  been  developed,  seems  to 
be  well  suited  to  a  hot  climate.  Major  Charles  E. 
Woodruff,  of  the  United  States  Army,  has  lately 
maintained  that  the  failure  of  the  white  races  to  col- 
onise the  tropics  is  due  to  the  excess  of  light  which 
there  prevails,  and  not  to  the  heat  or  humidity.  He 


THE  LIFE  OF  MAN  IN  THE  TROPICS  243 

believes  that  the  white  man,  especially  the  blond,  \ 
gradually  becomes  disinclined  to  work  on  this  ac- 
count, grows  neurasthenic,  and  finally  breaks  down. 
An  effect  of  climate  upon  the  kind  of  hair  has  also 
been  claimed,  but  on  this  point,  again,  Darwin  has 
noted  that  although  there  are  reasons  for  thinking 
that  the  growth  of  hair  is  affected  by  cold  and  damp- 
ness, he  had  "  not  yet  any  evidence  on  this  head  in 
the  case  of  man."  Schlagintweit  called  attention  to 
the  fact  that  the  inhabitants  of  Nepal  wore  much 
less  head-covering  than  Europeans,  and  did  not  suf- 
fer. The  sallow,  angemic  complexions  of  white  in- 
habitants of  the  tropics  are  a  subject  of  general 
comment. 

There  are  other  physiological  matters  which  must 
also  be  passed  over  without  discussion.  For  example, 
it  is  alleged  that  a  preponderance  of  females  in  warm 
climates  is  the  effect  of  the  light  diet  of  mothers  in 
the  tropics,  whereas  a  meat  diet  produces  more 
males.1  Direct  proof  of  the  assertion  that  sterility 
in  the  white  race  ensues  after  three  generations  in  the 
tropics  is  hard  to  find. 

The  Equatorial  Forests.  In  the  equatorial  belt 
we  find  the  hot,  sultry,  cloudy  conditions  of  the 
doldrums,  with  frequent  heavy  rains.  When  the 
doldrums  migrate  north  and  south,  and  the  trade 
winds  take  tjieir  place,  there  are  clearer  skies  for  a 
time,  and  little  or  no  rainfall.  There  are  two  rainy 
seasons  near  the  equator  (equatorial  type),  and  one 

1Schenck:   Einftuss  auf  das   Geschlechtsverhdltniss,  1898. 


244  CLIMATE 

rainy  season  farther  away  (tropical  type).  The  life 
of  man  in  the  equatorial  belt  as  a  whole  is  controlled 
by  the  rains.  The  dense  tropical  forests  of  equa- 
torial Africa,  South  America,  the  Malay  peninsula 
and  archipelago,  grow  where  the  rainfall  is  heaviest. 
These  forests  are  dark  and  depressing;  crowded  with 
creepers  and  plants  of  innumerable  varieties;  rich  in 
valuable  woods  such  as  mahogany,  ebony,  and  rose- 
wood; in  sap-products  such  as  rubber,  and  in  drugs 
such  as  quinine.  Poppig  has  compared  the  native 
South  American  tribes  with  their  forest  trees.  Man 
develops  rapidly  there,  as  does  the  vegetation.  He 
also  ages  rapidly,  like  the  tree  which  decays  at  the 
time  of  its  best  development.  The  tropical  tree  does 
not  strike  its  roots  firm  and  deep  into  the  soil;  it 
spreads  them  out  near  the  surface,  and  a  high  wind 
overturns  it.  So  it  is,  according  to  Poppig,  with  the 
native.  Both  he  and  his  trees  lack  the  stability  and 
endurance  of  northern  forests  and  of  temperate  zone 
man.  There  are  comparatively  few  animals  in  the 
dense  tropical  forests.  Reptiles,  birds,  and  mon- 
keys are  found.  The  large  mammals  are  in  the  more 
open  country. 

Such  a  superabundance  of  vegetation  is  unfavour- 
able to  human  occupation.  The  population  is  small, 
and  generally  at  a  very  low  stage  of  civilisation,  as 
illustrated  by  the  Indians  of  the  Amazonian  forests 
or  the  Pygmies  of  the  Congo,  who  wander  about  with- 
out settled  homes.  The  trees  and  undergrowth  act 
as  a  very  effective  barrier  to  the  advance  of  civilisa- 


TEE  LIFE  OF  MAN  IN  THE  TROPICS  245 

tion  from  the  margins  of  the  forest.  The  difficulty 
and  expense  of  travel  and  transportation,  and  of 
clearing  the  forest  for  purposes  of  agriculture,  oper- 
ate to  retard  the  advance  of  civilised  man.  The 
waves  of  civilisation,  as  one  writer  has  put  it,  beat  up 
against  the  forest,  but  only  occasionally  break 
through  it.  The  northern  forests  of  Argentina, 
inhabited  by  wandering  tribes  of  Indians;  the 
densely  wooded  Amazonian  provinces  of  Peru;  the 
equatorial  forests  on  the  west  coast  of  Africa;  the 
forests  of  Achin,  in  northern  Sumatra,  in  the  protec- 
tion they  have  afforded  the  natives  in  their  resistance 
against  the  Dutch;  the  eastern  forested  slopes  of 
Central  America,  left  longest  to  the  native  tribes, 
while  the  western,  more  open,  and  drier  slopes  were 
first  settled  by  white  men  and  are  best  developed— 
these  are  all  examples  of  the  repelling  effects  of  dense 
tropical  tree-growth  where  the  advance  of  civilised 
man  is  concerned.  Even  the  earlier  American  civil- 
isations, the  Aztec  and  the  Inca,  halted  before 
forested  areas.  It  has  been  pointed  out  that  the 
Incas  were  almost  as  much  hemmed  in  by  the  forests 
on  the  east  as  by  the  Pacific  on  the  west. 

In  the  equatorial  forests  the  men  hunt  and  fish; 
collect  rubber  or  other  forest  products;  do  a  little 
planting  in  the  forest  clearings,  without  paying  much 
attention  to  the  crop  when  planted.  By  clearing 
away  the  forest,  these  people  might  extend  the  area 
devoted  to  agriculture,  and  become  farmers.  In  the 
clearings  at  the  margins  of  the  forests  there  is  a  cer- 


246  CLIMATE 

tain  amount  of  agriculture,  carried  on  chiefly  by  the 
women,  who  are  also  occupied  with  domestic  duties 
while  the  men  are  hunting  or  fighting.  Settlements 
in  these  clearings  are  often  abandoned.  In  the 
Malayan  forest  the  natives  are  graded  from  those 
who  are  simple  nomads  to  those  who  have  settlements 
where  they  cultivate  rice  in  the  wet  jungles.  Rice 
needs  much  water,  and  its  cultivation  in  Java  is 
closely  allied  with  the  general  question  of  deforesta- 
tion. Where  the  sago  palm  grows,  and  provides 
food  without  the  need  of  much  labour,  the  natives  are 
least  advanced. 

Travel  through  the  forest  is  difficult.  Darwin 
thought  it  not  unlikely  that  the  habit  of  carrying 
knives  for  the  purpose  of  cutting  down  vegetation 
contributes  much  to  the  frequency  of  murder  among 
the  tropical  peoples.  Narrow  paths,  along  which 
travellers  move  in  Indian  file,  are  natural  ways  of 
communication  unless  travel  can  be  by  boat,  which  is 
obviously  quicker  and  easier.  The  natives  thus  nat- 
urally live  along  the  rivers.  It  has  been  pointed  out 
that  there  is  a  connection  between  the  method  of 
carrying  goods  in  the  African  forests,  on  the  backs  or 
heads  of  negro  porters,  and  the  slave  trade,  which 
sells  the  man  as  well  as  the  goods.  Many  of  the 
natives  who  secure  the  rubber  from  the  Amazonian 
forests,  or  from  those  of  the  Congo,  are  to-day  sub- 
jected to  hardships  which  equal  those  of  slavery. 

The  seasonal  floods  on  many  rivers,  the  Amazon 
for  example,  oblige  the  natives  to  build  huts  on  piles 


THE  LIFE  OF  MAN  IN  THE  TROPICS  247 

to  keep  them  above  the  water.  When  the  waters  rise 
higher  than  the  platforms,  the  people  take  to  their 
canoes,  until  the  flood  is  over.  In  some  places  the 
floods  drive  the  people  to  the  towns,  which  are  built 
on  natural  eminences.  In  New  Guinea  and  in  the 
Mosquito  Territory  the  natives  live  much  in  their 
boats  during  the  rainy  season.  In  fact,  in  the  former 
country  so  much  time  is  spent  on  the  water  that  the 
people  partly  lose  their  ability  to  walk.  They  al- 
most become  amphibious  beings.  Sir  Charles  Eliot 
reports  that  some  of  the  native  tribes  along  the 
Bahr-el-Gebel,  at  seasons  when  mosquitoes  are 
abundant,  use  platforms  on  poles  ten  or  twelve 
feet  high,  as  these  insects  do  not  fly  far  above  the 
ground. 

The  food  supply  along  the  Amazon  is  closely  re- 
lated to  the  rise  and  fall  of  the  water.  When  the 
river  is  in  flood,  the  turtles,  fish,  and  aquatic  birds 
migrate  to  the  northern  tributaries,  or  even  to  the 
Orinoco,  where  the  dry  season  is  on.  With  the  re- 
turn of  the  dry  season  on  the  Amazon  comes  the  op- 
portunity of  the  natives  to  catch  the  fish  and  turtles, 
and  to  secure  turtles'  eggs.  There  is  thus  a  very 
general  seasonal  migration  among  the  people.  The 
flood  time  is  the  time  of  deficient  food  supply.  This 
explains  the  origin  of  the  native  prayer  for  a  good 
dry  season,  ^he  conditions  of  life  on  the  Mosquito 
Coast  are  very  similar  (lat.  10°-15°  N.).  The 
north-east  trade  there  brings  the  dry  season 
(spring),  when  the  Indians  collect  the  eggs  of  alii- 


248  CLIMATE 

gators  and  turtles  on  the  dry  sand-banks.  Living- 
stone pointed  out  that  during  the  great  floods  in  the 
inland  lake  region  of  Africa  the  natives  live  upon, 
and  cultivate,  the  large  ant  hills,  in  the  Bangweolo 
and  Moero  districts.  On  the  plateau  of  western 
Nyassa,  the  Ba  Bisa  profit  by  the  heavy  rains  in  an 
interesting  way.  At  such  times  the  hollows  are 
swampy,  so  that  elephants  driven  into  them  become 
helpless  and  are  readily  killed.  Similarly,  as  reported 
by  Livingstone,  the  natives  of  the  islands  in  the  Zam- 
bezi River  utilise  the  floods  and  canoes  to  hunt  buf- 
faloes, these  animals  being  easily  caught  in  the  wa- 
ter. One  writer  has  pointed  out  that  certain  African 
tribes  purposely  go  naked  during  the  rains,  know- 
ing that  they  are  thus  less  likely  to  become  chilled. 

The  great  value  of  the  tropical  forest  products  is 
leading,  and  will  still  further  lead,  to  the  settlement 
of  considerable  numbers  of  whites  on  the  margins  of 
these  forests,  and  along  the  rivers  which  flow  through 
them.  Thus  in  Brazil,  along  the  lower  Amazon  and 
its  tributaries,  there  are  cacao,  sugar,  coffee,  tobacco, 
manioc,  and  rice  plantations ;  in  some  cases  also,  sugar 
factories,  rice  and  lumber  mills.  Large  cities  and 
towns  thus  gradually  grow  up,  like  Para  and  Manaos, 
and  the  native  tribes  come  more  and  more  into  con- 
tact with  civilisation. 

Travel  and  transportation  are  emphatically  con- 
trolled by  climate  throughout  the  equatorial  belt. 
Roads  become  almost  or  quite  impassable  during  the 
rainy  season.  Lowlands,  as  in  central  Africa  and  in 


THE  LIFE  OF  HAN  IN  THE  TROPICS  249 

equatorial  South  America,  turn  into  swamps  or  tem- 
porary lakes,  so  that  all  travel  may  be  stopped.  In 
other  places,  where  boats  are  used  at  all  seasons,  the 
rains  give  high  water  and  aid,  rather  than  hinder, 
travel.  The  control  of  the  floods  of  the  Chagres 
River,  on  the  Isthmus  of  Panama,  is  one  of  the  most 
difficult  problems  with  which  the  engineers  have 
dealt.  Work  on  railroads  is  always  much  interfered 
with  during  the  rainy  season,  if  not  interrupted 
altogether.  Dense  tropical  vegetation  seriously 
obstructs  railroad  construction  and  operation.  The 
roadway  is  constantly  being  overgrown,  and  men 
must  be  kept  at  work  cutting  down  the  weeds,  under- 
brush, and  trees.  This  involves  great  expense,  and 
seriously  reduces  the  earnings  of  the  roads.  Recently, 
tank-cars  which  frequently  spray  the  right  of  way 
with  a  strong  poison  have  come  into  use,  as  on 
the  Guayaquil-Quito  line  in  Ecuador,  and  on  the 
Tehuantepec  Railroad.  Ties  and  trestles  rot  quickly, 
or  are  destroyed  by  insects.  Special  kinds  of  ties, 
such  as  lignum  vitce,  or  camphor  wood,  or  even  iron, 
have  therefore  been  used.  Although  vegetation  is 
thus  a  serious  handicap  to  railroads  in  the  moist 
tropics,  it  serves  a  useful  purpose  in  preventing  the 
sides  of  steep  cuts  from  sliding  down.  The  absence 
of  frost  makes  possible  cuts  with  steeper  sides  than  in 
colder  latitudes.  Along  the  older  portion  of  the 
Panama  Canal,  which  has  been  built  for  some  years, 
no  masonry  was  needed  to  keep  the  banks  from  cav- 
ing in.  The  heavy  vegetation  served  the  purpose  of 


250  CLIMATE 

stone  and  cement.  Fevers  and  other  diseases  com- 
mon in  the  rainy  season  of  the  tropics  are  also  a  seri- 
ous handicap,  and  floods  and  landslides  add  to  the 
difficulties.  The  sultry  heat  is  another  obstacle. 
Curious  complications  in  the  employment  of  several 
different  kinds  of  labour  arose  on  the  Uganda 
Railway.  For  four  castes  among  the  Indian  work- 
men, four  separate  water-tanks  had  to  be  provided, 
and  if  the  water  in  one  tank  gave  out,  that  particular 
one  had  to  be  sent  by  train  to  be  filled,  although  the 
remaining  three  tanks  were  full.  Dr.  H.  R.  Mill 
has  pointed  out  that  there  are  many  features  on  the 
Uganda  Railway  which  show  climatic  control.  The 
cars  are  built  of  metal,  in  order  to  defy  wood-boring 
insects.  They  have  deep  ventilators,  protected  by 
wire  gauze  against  mosquitoes.  The  windows  are  of 
green  glass  to  give  protection  against  the  glare  of 
the  sun. 

During  the  dry  season  the  difficulties  are  similar  to 
those  noted  later  under  deserts.  At  that  time  dust 
makes  travelling  disagreeable,  and  instead  of  streams 
being  impassable,  they  often  dry  up,  and  their  beds 
serve  as  roads. 

A  curious  relation  of  thunder-storms  and  naviga- 
tion is  reported  by  Hann  from  Maracaibo,  Venez- 
uela. The  lightning  flashes  from  rainy-season 
thunder-storms  at  the  south-western  end  of  the  lake 
of  Maracaibo  are  used  by  captains  in  navigating  their 
vessels  through  the  strait  of  Maracaibo.  "  El  Faro 
de  Maracaibo,"  as  these  lightnings  are  locally  called, 


THE  LIFE  OF  MAN  IN  THE  TROPICS  251 

gives  a  good  compass-direction  for  steering  a  ship  on 
dark  nights. 

The  Open  Grass  Lands  of  the  Tropics:  Savannas. 
Between  the  forests  on  one  side  and  the  deserts  on  the 
other  comes  a  transition  zone  of  moderate  rainfall. 
Here  the  forests  are  replaced  by  an  intermediate  belt 
of  more  or  less  open,  grassy  country,  known  as  the 
savanna.  There  are  usually  a  long  dry  and  a  shorter 
wet  season  (summer).  Vegetation  has  but  a  short 
season  for  growth.  Savannas  are  found  in  Africa 
and  in  South  America  both  north  and  south  of  the 
equator.  In  Africa  they  include  the  Sudan;  in 
South  America,  the  llanos  of  Venezuela  and  the  cam- 
pos  of  Brazil;  in  Australia,  the  downs.  The  open 
country  and  the  grass  cover,  which  forms  natural  hay 
in  the  dry  season,  fit  the  savannas  for  grazing  pur- 
poses. The  people  are  essentially  pastoral.  Popu- 
lation is  denser  than  in  the  tropical  forest,  and  the 
people  are  more  energetic  and  more  advanced.  The 
African  savannas  are  abundantly  supplied  with  large 
animals  such  as  lions,  tigers,  antelopes,  elephants, 
rhinoceroses,  and  giraffes. 

Their  dependence  upon  grass  and  water  for  their 
cattle  forces  the  inhabitants  of  the  savannas  to  be 
more  or  less  nomadic,  the  more  so  the  more  pastoral 
the  people  are.  They  move  their  tents  and  household 
goods  easily  over  great  distances,  stopping  where 
there  are  pasturage  and  water.  Their  food  is  supplied 
chiefly  from  their  flocks  and  herds,  of  cows,  goats,  or 
camels.  Agriculture  of  a  somewhat  primitive  kind 


252  CLIMATE 

is  often  combined  with  grazing  in  the  better-watered 
portions  of  the  savannas,  the  seed  being  sown  at  the 
beginning  of  the  rains.  The  population  there  be- 
comes more  sedentary.  Thus  in  the  Sudan  there  is 
a  belt  of  agriculture  nearer  the  equator,  where  the 
rainfall  is  heavier,  and  a  pastoral  zone  farther  from 
the  equator,  where  there  is  less  rainfall.  In  these 
districts  the  rainfall  varies  much  from  year  to  year, 
and  there  are  frequent  droughts  and  famines. 
Thousands  of  persons  may  then  die  of  starvation,  as 
has  happened  in  parts  of  the  Sudan,  in  Nubia,  and 
elsewhere  within  a  few  years.  At  such  times  the 
cattle  die  in  large  numbers,  and  where  the  herds  have 
been  lost  by  famine  or  disease  it  has  happened  that 
certain  native  tribes  (e.  gtj  the  Galla,  in  eastern 
Africa),  after  suffering  terribly  from  hunger,  have 
changed  their  place  of  residence,  turning  in  part  to 
plunder  and  hunting,  and  in  part  to  farming.  A 
curious  case  of  seasonal  migration  into  the  desert  has 
been  reported  of  the  Tuaregs,  who  inhabit  part  of  the 
region  about  Lake  Chad.  The  upper  class  of  these 
people  is  nomadic,  and  during  the  rainy  season  re- 
tires into  the  desert  with  its  camels,  which  do  not 
like  the  rains. 

All  the  savannas  will  in  time  be  more  thickly  popu- 
lated and  more  valuable  than  now,  owing  to  the 
availability  of  considerable  portions  of  them  for  agri- 
culture, especially  where  irrigation  can  be  practised. 
Under  the  supervision  of  white  overseers,  the  natives 
will  become  better  agriculturists  and  cattle-raisers. 


THE  LIFE  OF  MAN  IN  THE  TROPICS  253 

In  South  America,  as  well  as  in  Australia,  the  sa- 
vannas are  in  part  being  sown  to  wheat.  From  the 
savannas  and  the  neighbouring  deserts,  ivory,  ostrich 
feathers,  palm  oil,  dates,  gums,  and  so  on,  are 
secured. 

Trade  Wind  Belts  on  Land:  the  Deserts.  The 
major  part  of  the  earth's  surface  in  the  trade  wind 
belts  is  a  desert,  which  forms  a  marked  feature  of 
every  rainfall  map  of  the  world.  These  trade  wind 
deserts,  because  of  their  great  extent,  are  of  immense 
importance  from  a  human  standpoint.  They  are 
belts  of  scanty  population.  They  form  great  bar- 
riers, across  which  even  to-day  travel  and  transporta- 
tion are  difficult  and  expensive.  The  interior  of 
Africa  has  been  out  of  contact  with  the  civilised  world 
largely  because  of  the  deserts  to  the  north  and  south 
of  it.  Goods  and  passengers  go  around,  rather  than 
across  them.  Trails  across  the  desert  are  easily 
effaced  by  blowing  sand,  or  are  shifted  as  some  oasis 
dries  up.  Along  their  margins,  where  there  is  a 
moderate  rainfall,  or  where  oases,  wells,  or  streams 
make  permanent  settlement  possible,  the  population 
is  more  or  less  sedentary,  agricultural,  pastoral,  and 
commercial,  but  even  here  droughts  and  famines  may 
occur,  and  agriculture  is  not  absolutely  sure.  Riv- 
ers which  cross  the  desert  gain  their  water  from  the 
rainier  lands  beyond,  and  then  flow  long  distances 
without  tributaries.  The  Nile  is  the  classic  example 
of  this.  Along  such  rivers  population  naturally 
gathers ;  irrigation  and  agriculture  are  practised,  and 


254  CLIMATE 

the  entire  valley  becomes  an  oasis.  The  Nile  and  the 
rivers  of  the  coastal  desert  of  South  America  are 
illustrations;  in  the  Deccan,  also,  the  river  systems 
are  the  centres  of  the  densest  population.  It  is  dif- 
ficult to  overestimate  the  effect  which  the  Nile  had 
upon  the  civilisation  of  ancient  Egypt.  It  has  been 
asserted  with  good  reason  that  the  annual  overflow, 
by  depositing  silt  and  by  wiping  out  the  boundaries 
of  individual  tracts  of  land,  obliged  the  ancient 
Egyptians  to  develop  mathematical  skill  in  re-sur- 
veying these  lands,  as  it  also  led  to  canal  and  dam 
building.  Where  deserts  are  irrigated,  it  is  some- 
times necessary  to  guard  the  water  supply,  as  in  Chile 
and  Peru. 

In  the  desert  proper,  a  nomadic  life  and  a  scat- 
tered population  are  characteristic  and  inevitable  re- 
sults of  the  aridity.  As  Schirmer  has  expressed  it, 
"  the  purer  the  desert,  the  more  the  inhabitants  dis- 
perse themselves."  The  Saharan  nomads  camp  for 
a  few  months  in  winter,  it  may  be  near  the  towns, 
and  then  travel  with  their  flocks  in  summer.  The 
Bedouins,  although  they  wander  to  and  fro  over  a 
wide  area,  nevertheless  keep  within  certain  recog- 
nised limits.  In  the  desert,  population  gathers 
in  the  oases,  as  on  islands.  Here  the  trails  followed 
by  the  caravans  come  together,  like  sailing  routes  at 
sea.  Thus  there  is  naturally  developed  a  settlement, 
in  which  the  people  are  in  places  so  crowded  that 
they  may  be  on  the  verge  of  starvation  all  the  time. 
There  are  small  Arabian  towns  wrhere  the  houses  are 


THE  LIFE  OF  MAN  IN  THE  TROPICS  255 

almost  crowded  on  top  of  one  another,  producing 
something  not  unlike  the  modern  "  sky-scraper  "  of 
an  American  city,  where  land  is  scarce  and  expensive. 
When  such  oases  dry  up,  or  are  encroached  upon  by 
the  desert  sands,  they  are  abandoned,  and  the  ruins, 
later  discovered  by  some  explorer,  give  the  impres- 
sion of  a  diminishing  population. 

The  climate  of  the  trade  wind  deserts  is  drier  and 
more  stimulating,  and  has  larger  temperature  ranges, 
than  that  of  the  forests  and  of  the  savannas.  The 
need  of  protection  against  heat  and  cold  is  greater; 
food  more  difficult  to  obtain;  life  a  harder  struggle. 
Therefore  the  desert  produces  more  active,  more 
energetic,  and  more  progressive  men.  They  are  inde- 
pendent, bold,  and  strong.  Nachtigal  has  pointed 
out  the  difference  between  the  healthy  and  vigorous 
tribes  of  the  Sahara  and  the  less  active  Sudanese. 
The  hardy,  warlike  inhabitants  of  the  desert  of  Per- 
sia and  Baluchistan  have  frequently  held  in  subjec- 
tion the  people  of  the  richer  lowlands  on  the  west. 
There  is  a  well  recognised  difference  between  the  true 
nomad  desert-dweller  and  the  weaker  sedentary. 
From  the  latter,  the  former  often  takes  tribute,  and 
if  the  exactions  become  unbearable,  the  unfortunate 
sedentary  farmer  may  be  forced  in  self-defence  to  be- 
come a  nomad  himself.  The  nomadic  life  of  the  des- 
ert-dwellers tends  to  make  robbers  of  them,  so  that 
pillaging  of  caravans  is  not  an  uncommon  occurrence. 
The  utter  hopelessness  of  the  isolated  Australian 
desert  seems  to  have  led  to  a  most  degraded  condition 


256  CLIMATE 

among  its  inhabitants.  Nearly  naked,  living  on  the 
lowest  forms  of  desert  life,  and  practising  cannibal- 
ism and  the  murder  of  the  weak  and  helpless,  they 
have  ranked  among  the  lowest  human  beings  in  the 
world. 

The  trade  wind  deserts  are  gaps  in  the  map  of  the 
world's  civilisation.  When  the  tribes  or  individu- 
als who  live  along  the  margins  of  the  deserts  are 
forced  into  the  deserts,  they  tend  to  scatter  and  dis- 
appear. There  are  also  migrations  out  from  the  des- 
ert into  the  more  fertile  regions  adjoining,  as  in  the 
case  of  the  Tuaregs  in  the  Sudan.  The  advance  of 
the  nomadic  Arabs  from  the  Sahara  into  the  lands  of 
the  more  peaceable  agricultural  negroes  to  the  south 
has  been  compared  with  the  encroachment  of  the 
desert  sands  over  some  fertile  grass-covered  land 
along  its  border. 

The  more  permanent  dwellings  often  have  flat 
roofs,  and  are  built  of  stone  or  adobe,  wood  and  vege- 
table products  being  scarce  or  entirely  lacking.  Slop- 
ing roofs  are  not  needed,  as  the  protection  desired  is 
not  against  rain,  but  against  sun  and  wind.  In  hot, 
dry  climates  the  flat  roofs  are  generally  used  for 
sleeping  at  night.  The  houses  are  low,  sometimes 
even  partly  underground,  for  better  protection 
against  the  wind.  When  the  people  are  on  the  move 
tents  are  taken,  made  of  skins  or,  where  the  materials 
are  obtainable,  of  thatch,  palm  leaves,  or  grass.  The 
timber  usually  comes  from  the  date  tree.  On  the 
arid  west  coast  of  South  America  the  Incas  used 


THE  LIFE  OF  MAN  IN  THE  TROPICS  257 

adobe  bricks  chiefly  in  the  regions  with  least  rainfall, 
and  granite  and  porphyry  on  the  rainier  plateaus. 
Even  the  great  Inca  temples,  built  of  massive  stone 
blocks,  had  light  thatched  roofs,  because  but  little  pro- 
tection against  rain  was  necessary.  In  the  Chilean 
desert  many  of  the  richest  mines  were  discovered  in 
the  early  days  by  men  who  were  hunting  for  firewood 
or  tending  cattle. 

The  nights  are  often  cool,  and  heavier  clothing  is 
worn  than  by  day.  Both  clothing  and  food  are 
simple,  and  are  supplied  chiefly  from  the  flocks  and 
herds,  which  are  the  desert  inhabitants'  most  precious 
possession,  or  from  desert  plants,  such  as  the  date. 
Along  the  shores  of  the  Persian  Gulf,  where  there  is 
no  wood  supply,  even  boats  are  made  of  date  leaves. 
The  dry  desert  air  preserves  rather  than  destroys. 
Sun-dried  meat  may  become  an  article  of  food,  as  in 
the  charqui  of  Peru.  Livingstone  and  others  have 
noted  that  the  desert  peoples  of  Africa  are  much  less 
clean  than  those  who  inhabit  the  moister  parts  of  the 
tropics.  The  lack  of  water,  as  well  as  the  belief  that 
water  makes  the  skin  sensitive  to  the  heat,  leads  to  a 
great  lack  of  cleanliness.  In  Abyssinia,  Nubia,  and 
elsewhere,  a  kind  of  sand  bath  is  substituted  for  the 
usual  bath  with  water.  Protection  against  dust  and 
sun  is  found  by  covering  the  head  and  wearing  a  veil, 
as  is  done,  for  example,  by  the  Tuaregs,  who  are  com- 
pletely covered  with  the  exception  of  their  eyes. 
Some  tribes  blacken  their  eyelids  and  their  faces,  just 
as  is  done  by  people  in  the  Himalayas  as  a  protection 

»7 


258  CLIMATE 

against  snow-blindness.  During  dust  storms  and 
high  winds  all  protection  may  be  inadequate,  and 
death  may  result. 

Utensils  of  all  sorts  are  made  chiefly  of  leather. 
In  Nubia,  as  reported  by  Speedy,  baskets  are  so 
closely  woven  of  leather  strips  that  they  are  fluid- 
proof.  As  these  cannot  be  placed  on  the  fire,  milk 
is  warmed  by  dropping  red-hot  stones1  into  them. 
Many  desert  people  become  adepts  at  plaiting  and 
weaving  in  leather.  Well-digging  is  an  occupation 
in  which  many  of  the  Saharans  have  by  nature  been 
forced  to  become  skilled.  Here  and  there  salt,  nitrate, 
or  borax  deposits  locally  give  an  exceptional  eco- 
nomic value  to  the  desert,  and  furnish  employment  tQ 
many.  Salt  may  become  an  important  article  of  ex- 
change. The  amount  of  nitrate  exported  from 
Chile  is  determined  largely  by  the  weather  and  crop 
conditions  of  Europe. 

That  deserts  have  had  a  significant  relation  to  re- 
ligious ideas  has  been  suggested  by  several  writers. 
Ernest  Renan  points  out  that  the  desert  is  mono- 
theistic, its  uniformity  suggesting  a  belief  in  the  unity 
of  God.  The  desert  is  conducive  to  a  solitary,  medi- 
tative life;  even  to  a  morbid  and  fanatical  state  of 
mind.  Such  conditions,  it  is  believed,  furnished  good 
ground  for  the  growth  of  such  a  religion  as  Moham- 
medanism. In  his  Seas  and  Skies  in  Many  Lati- 
tudes (London,  1888,  pp.  42-43),  Abercromby 
gives  two  maps,  showing  respectively  the  areas  of 


THE  LIFE  OF  MAN  IN  THE  TROPICS  259 

Mohammedanism  and  the  districts  in  Asia  and 
Africa  with  a  mean  annual  rainfall  of  less  than  ten 
inches.  The  maps  are  strikingly  similar.  The 
author  adds:  "Whether  this  distribution  of  a  great 
creed  is  the  result  of  chance,  or  of  some  deep  connec- 
tion between  the  tenets  of  that  religion  and  climatic 
influences,  I  cannot  say;— but  still  the  relation  is  so 
remarkable  that  I  have  thought  it  well  to  bring  the 
matter  forward."  The  rain-ceremonies  and  rain- 
dances  among  the  native  tribes  of  central  Australia; 
the  Indian  celebrations  of  the  rise  of  water  in  the 
Peruvian  rivers;  the  ancient  Aztec  sacrifices  to  the 
god  of  rain  in  Mexico,  and  other  similar  customs  in 
tropical  deserts,  are  natural  in  a  region  where  water 
is  of  supreme  importance.  In  one  of  the  Australian 
rain-ceremonies,  the  men  dance  around  a  mimic  water- 
hole,  imitating  the  calls  and  motions  of  aquatic  ani- 
mals. These  dances  are  reported  as  being  carefully 
timed,  by  experienced  individuals,  to  come  at  the 
seasons  when  rain  is  likely  to  fall. 

The  night  is  cooler  and  less  dusty  than  the  day, 
and  is  the  best  time  for  travelling.  The  camel,  which 
can  go  long  without  food  and  water,  is  the  natural 
beast  of  burden.  Trade  is  still  largely  carried  on  by 
means  of  caravans,  which  require  camels  and  driv- 
ers, and  give  employment  to  many  men.  The  con- 
struction of  railroads  across  these  deserts  will  present 
the  same  difficulties  which  have  already  been  met 
in  the  arid  regions  of  the  temperate  zone.  Ties  dry 


260  CLIMATE 

up  and  twist;  the  danger  from  fire  is  greatly  in- 
creased, often  necessitating  fire  patrols;  fuel  is  ex- 
pensive and  must  be  imported,  unless  a  poor  local 
fuel,  like  sheep  or  llama  dung,  is  used;  water  for  men 
and  locomotives  must  be  brought  in  by  water-trains, 
tank  cars,  or  pipe  line,  or  locally  distilled,  at  consid- 
erable expense;  cloud-bursts  sweep  away  bridges  and 
tracks;  the  number  of  working  hours  by  day  is  re- 
duced by  the  heat;  drifting  sands  cover  the  track  and 
must  constantly  be  shovelled  off;  the  blowing  sand 
hinders  seeing,  and  increases  friction  and  wear  on  the 
rolling  stock;  watchmen  to  guard  against  accidents 
from  blowing  sand  on  the  track  must  be  employed; 
proper  non-dusty  ballast  is  difficult  to  secure;  all 
lumber  must  be  brought  from  moister  regions.  On 
the  other  hand,  the  trade  wind  deserts  are,  on  the 
whole,  healthy  regions.  When  the  Sahara  and  the 
Australian  desert  are  bridged  by  railroads,  and  when 
the  South  American  coastal  desert  is  traversed  by  a 
longitudinal  line  of  track  from  north  to  south,  the 
relations  of  these  great  arid  regions  to  man  will  in- 
evitably be  greatly  changed. 

Trade  Belts  at  Sea.  At  sea,  the  trade  wind  belts 
are  closely  related  to  man  through  their  control  over 
sailing  routes,  and  over  voluntary  and  involuntary 
migrations.  A  glance  at  any  pilot  chart  will  show 
that  all  sailing  routes  which  pass  through  the  trade 
wind  belts  in  any  ocean  are  determined  by  the  course 
of  these  winds.  The  route  from  Europe  to  India 
furnishes  a  good  example  of  the  advantage  that  is 


THE  LIFE  OF  MAN  IN  THE  TROPICS         261 

taken,  by  mariners  of  the  present  day,  of  the  prevail- 
ing wind  systems  of  the  world.  In  former  times  a 
vessel  was  kept  close  in  along  the  west  coast  of 
Africa,  amid  calms  and  adverse  winds,  and  then,  after 
passing  the  Cape  of  Good  Hope  and  leaving  Moz- 
ambique, she  waited  for  the  blowing  of  the  south-west 
monsoon,  with  which  she  continued  her  voyage  to 
India.  In  1500,  Cabral  sailed  from  the  Cape  Verde 
Islands  out  into  the  open  sea  with  the  north-east 
trades,  avoiding  the  African  coast.  Keeping  far  to 
westward  he  discovered  Brazil;  continued  across  the 
south-east  trade,  rounded  the  Cape  of  Good  Hope 
with  the  westerlies,  and  then  proceeded  up  the  east 
coast  of  Africa  as  had  previously  been  the  custom. 
In  the  17th  century  the  Dutch  struck  off  on  the  new 
route  from  the  Cape  of  Good  Hope,  making  their 
easting  in  the  prevailing  westerly  winds  of  the  South 
Indian  Ocean,  and  then  sailing  up  to  India  with  the 
south-east  trade.  The  passage  across  the  equatorial 
belt  of  calms  (doldrums),  which  was  formerly  much 
dreaded,  is  now  so  carefully  worked  out  that  vessels 
may  cross  where  the  belt  is  narrowest,  and  where 
there  is  therefore  the  least  danger  of  delay. 

Steady  winds  like  the  trades  certainly  tempted  the 
early  navigators  to  put  to  sea.  The  famous  voyage 
of  Columbus,  when  he  discovered  America,  was  fa- 
cilitated, if  pot  made  possible,  by  the  north-east  trade. 
The  easy  outward  voyages  of  the  early  Spanish 
adventurers  and  colonists  took  them  naturally  to  that 
portion  of  the  Americas  where  they  found  climates  in 


262  CLIMATE 

which  they  and  their  descendants  could  live,  while  to 
the  Anglo-Saxon  originally  fell  the  North  American 
continent,  with  its  more  rigorous  climate.  The 
monsoons  of  India  have,  from  the  earliest  days  of 
trade  with  the  East,  been  important  agents  in  aiding 
commerce.  In  the  Mediterranean,  the  Etesian  winds 
—the  northward  extension  of  the  trade — favoured 
early  commerce.  The  migrations  of  the  Malays 
to  the  Melanesian  Islands,  of  the  Polynesians, 
and  of  other  Pacific  islanders,  found  their  occasion 
and  their  possibility  in  the  prevailing  winds  of  those 
latitudes.  The  islands  from  the  Philippines  to  the 
Gilbert  Islands  are  in  the  north-east  trade  and  from 
the  Moluccas  to  the  Society  Islands  in  the  south-east 
trade.  Thus  intercourse  and  migrations  are  easy.  In 
the  archipelago  of  the  monsoon  belt  south-east  of  Asia 
trade  depends  largely  upon  monsoons.  An  inter- 
esting case  is  cited  by  Ratzel,  on  the  authority  of  von 
Maltzan.  Two  small  ports,  Bir  Ali  and  Megdaha, 
lie  opposite  one  another  on  the  southern  coast  of 
Arabia,  in  a  small  bay.  The  former  is  protected  on 
the  west,  and  the  latter  on  the  east.  Hence  the  former 
is  sought  by  shipping  in  summer,  and  the  latter  in 
winter.  Both  places  have  grown  and  really  make  one 
town,  the  officials  and  many  of  the  inhabitants  mov- 
ing twice  a  year  with  the  seasonal  change  of  wind. 
The  war  expeditions  of  the  native  tribes  of  this 
great  island  region  have  always  been  governed  by  the 
monsoons.  In  many  places  to-day  native  boats  do 
not  venture  to  sea  at  the  height  of  the  monsoon.  In 


THE  LIFE  OF  MAN  IN  THE  TROPICS         263 

the  discussions  regarding  the  relative  advantages  of 
the  Nicaragua  and  Panama  Canal  routes,  much  em- 
phasis was  laid  upon  the  prevailing  winds  in  the  two 
cases.  Many  of  the  optimistic  predictions  concern- 
ing the  use  of  the  Panama  Canal  by  sailing  ves- 
sels did  not  take  account  of  the  calms  and  variable 
or  adverse  winds  to  be  encountered  before  entering 
and  on  leaving  the  canal,  which  necessitate  trans- 
portation by  steamer,  or  at  least  some  towing  of 
sailing  vessels. 

To  leeward  of  the  west  coast  of  Africa  navigation 
is  not  infrequently  interfered  with  by  the  so-called 
"  tornadoes,"  which  move  westward  off  the  land,  and 
by  dust-storms,  which  obscure  the  air  and  delay 
progress. 

Tropical  cyclones  at  certain  seasons  and  in  certain 
parts  of  the  trade  wind  belts  at  sea  not  only  damage 
shipping,  but  often  devastate  towns,  bridges,  and 
crops,  bringing  starvation,  poverty,  and  not  infre- 
quently pestilence  as  well,  owing  to  decaying  animal 
matter,  or  fish  thrown  up  by  the  sea.  Thousands 
of  lives  have  been  lost  as  the  result  of  such  disasters. 
The  Pacific  islands  are  particularly  unfortunate  in 
this  respect.  The  storm  waves  produced  by  these 
cyclones  are  especially  severe  at  the  head  of  the  Bay 
of  Bengal.  Native  huts  are  easily  blown  over  by 
the  cyclonic  winds,  and  it  has  been  pointed  out  that 
the  huts  elevated  on  high  posts  in  New  Guinea,  and 
swaying  with  the  wind,  furnish  good  evidence  that 
the  district  in  which  they  are  found  is  not  visited  by 


264  CLIMATE 

tropical  cyclones.  In  some  places,  Mauritius,  for 
example,  houses  are  provided  with  shutters  to  be  used 
in  case  of  a  cyclone,  and  in  many  places  the  natives 
have  resistance  to  cyclones  in  mind  when  they  build 
their  huts.  In  time,  buildings  must  be  erected  in  the 
tropics  which  will  withstand  these  storms  better. 
Worcester  reports  of  the  Philippines  that  in  order  to 
save  the  banana  trees  from  destruction  by  typhoons, 
some  of  the  natives  cut  off  all  the  larger  leaves  when 
the  approach  of  a  typhoon  becomes  evident. 

Monsoon  Districts.  Of  the  monsoon  districts  on 
land,  India  is  the  largest  example.  The  two  seasons 
are  strongly  contrasted.  The  success  or  failure  of 
the  crops  depends  upon  the  amount,  distribution,  and 
time  of  occurrence  of  the  summer  monsoon  rains. 
Famine  follows  when  these  rains  are  deficient  or  un- 
favourably distributed,  with  terrible  suffering  and 
the  loss  of  thousands  of  lives  among  men  and  cattle. 
Lately  the  government  of  India,  at  great  expense, 
has  undertaken  relief  works  during  times  of  famine, 
including  irrigation  works.  The  amount  and  regu- 
larity of  the  water  supply  is  the  chief  factor  in  deter- 
mining the  density  of  population  in  India. 

Travel  and  transportation  in  monsoon  districts  de- 
pend closely  upon  the  season.  During  the  rains,  the 
roads  are  likely  to  be  bad  or  impassable,  and  land- 
slides and  washouts  are  common.  In  the  Philippines 
the  mud  is  so  deep  that  sledges  are  used  instead  of 
wheeled  vehicles.  Communication  may  be  entirely 
interrupted  by  floods.  Campaigning  under  such 


THE  LIFE  OF  MAN  IN  THE  TROPICS         265 

conditions  is  extremely  difficult,  as  was  abundantly 
proved  during  the  American  occupation  of  the 
Philippines.  Horses,  and  even  water-buffaloes,  were 
often  unable  to  haul  the  guns,  one  of  the  difficulties 
with  the  buffaloes  being  their  need  of  a  mud  bath  in 
the  hottest  part  of  the  day.  During  the  early  part  of 
the  American  campaign  in  the  Philippines  the  success 
of  the  American  army  was  achieved  in  the  dry  sea- 
sons, the  natives  gaining  the  upper  hand,  or  at  least 
making  the  most  progress,  during  the  rains,  when 
conditions  were  hardest  for  the  white  men. 

Native  dwellings  are  adapted  to  the  different  sea- 
sons, as  on  the  island  of  Mindoro,  where  the  Mangy- 
ans  erect  simple  shelters  of  rattan  and  leaves  wherever 
they  happen  to  be  in  the  dry  season,  while  in  the  rainy 
season  the  dwellings  are  more  elaborate  and  more  se- 
cure. The  rain  hat  and  coat  of  the  Filipinos;  the 
preparations  made  in  north-western  Mysore,  on  the 
summit  of  the  western  Ghats,  in  laying  in  provisions 
to  last  during  the  long  rainy  season,  as  if  it  were  for 
an  extended  voyage  at  sea;  the  general  use  of 
punkahs,  tatties,  grass  mats,  etc.,  for  cooling  pur- 
poses during  the  hot  and  dry  season  in  India  and 
Persia,  these  being  often  wet,  and  kept  in  motion  by 
coolies;  the  habit  of  closing  houses  during  the  day 
and  of  staying  indoors  during  the  hottest  hours,— 
these  few  cases  may  suffice  to  illustrate  the  con- 
trol of  climate  over  the  life  of  man  in  the  monsoon 
belts. 

Tropical  Mountains.     Their  "  temperate  "  climates 


266  CLIMATE 

have  given  many  tropical  mountains  and  plateaus  a 
deserved  popularity,  and  the  increasing  settlement 
of  the  tropics  by  white  men  and  women  will  constant- 
ly tend  to  bring  such  elevations  into  greater  use. 
Under  these  conditions  the  usual  law  of  the  decrease 
of  population  with  increase  of  altitude  is  locally  re- 
versed, at  least  up  to  a  certain  height.  Mountains 
within  the  polar  zones  do  not  increase  the  habitable 
parts  of  the  earth's  surface.  Mountains  within  the 
tropics  certainly  give  white  men  and  women  a  larger 
area  and  more  comfortable  conditions  of  habitability. 
There  is  observable  a  tendency  for  the  altitude  of 
human  settlements  to  increase  from  polar  latitudes 
towards  the  equator.  In  the  far  north  man  lives  close 
to  sea-level ;  within  and  near  the  tropics  there  is  often 
a  large  population  at  considerable  altitudes,  as  in  the 
Himalayas  and  on  the  Andean  plateaus.  In  parts  of 
South  America  at  the  present  day  (e.  gfj  Colombia) 
the  plateaus  are  the  chief  seat  of  the  Spanish  and 
Spanish-Indian  population,  and  the  lowlands  are  oc- 
cupied by  the  negroes.  The  talk  of  removing  the  Bra- 
zilian capital  from  Rio  de  Janeiro  to  a  more  elevated 
location  in  the  interior  province  of  La  Goyaz,  and 
the  government  offices  of  the  Italian  colony  of  Eritrea 
from  Massowa,  on  the  Red  Sea,  to  the  high  plateau 
of  the  Hinterland,  shows  the  upward  tendency  of 
the  white  man  in  the  tropics.  On  the  other  hand, 
the  production  of  sugar-cane,  coffee,  and  other  valu- 
able products  will  obviously  lead  more  and  more  to 
the  development  of  the  lowlands  under  white  control. 


TEE  LIFE  OF  MAN  IN  THE  TROPICS        267 

To  the  greatest  altitudes  man  is  attracted  by  mineral 
wealth,  and  lives  under  very  hard  conditions.  Some 
of  the  Tibetans  live  more  or  less  underground,  and 
melt  ice  in  order  to  secure  water.  High  mountains 
within  the  tropics  show  a  vertical  succession  of  cli- 
mates from  tropical  at  their  base  to  eternal  snow  on 
their  summits.  A  very  striking  illustration  of  this 
may  be  secured  by  a  passenger  who  travels  over  the 
famous  Oroya  Railroad,  in  Peru.  This  road  runs 
from  sea-level  to  a  height  of  15,665  feet,  and  then  de- 
scends again  to  about  12,000  feet.  The  first  part  of 
the  journey  is  through  fields  of  sugar-cane  and  cot- 
ton ;  at  about  5000  feet  a  zone  of  fruit  trees  is  passed 
through;  at  10,500  feet  there  is  a  district  famous  for 
its  potatoes,  where  little  else  is  grown;  above  this,  the 
altitude  is  so  great  as  to  preclude  the  growth  of  any- 
thing but  grass.  At  the  highest  point  reached,  the 
snow  lies  on  the  mountain  summits  throughout  the 
year,  and  the  traveller  may  enjoy  a  snowstorm  in  the 
middle  of  summer  (December-February) .  In  the 
interior  valley,  farm  produce  is  again  seen  growing. 
This  whole  succession  of  climates  may  be  passed 
through  in  the  short  space  of  ten  hours.  Tropical 
mountains  may  thus  produce  temperate  zone  crops. 
In  the  deserts,  mountains  may  be  covered  with  for- 
ests and  other  vegetation,  by  reason  of  the  rainfall 
which  they  provoke.  Here  man  naturally  settles, 
finding  water  and  perhaps  favourable  conditions  for 
agriculture.  Such  mountains  become  "  islands  "  of 
denser  population,  as  do  the  streams  which  run  out 


268  CLIMATE 

from  them  to  wither  away  in  the  desert.  In  Dar 
Fur,  in  the  eastern  Sudan,  most  of  the  inhabitants 
live  in  or  near,  and  in  close  dependence  upon, 
the  Marra  Mountains.  Kilimanjaro,  in  equatorial 
Africa,  rises  as  an  island  above  the  surrounding 
steppes,  and  is  in  the  centre  of  a  large  population. 
At  the  southern  foot  of  the  Atlas  Mountains  there 
are  three  ethnological  zones,  from  the  nomadic  desert- 
dwelling  Tuareg  to  the  Berber  tribes  scattered  in  the 
mountains,  with  a  denser  population  in  the  strip  of 
oasis  between. 

The  permanent  physiological  effects  of  tropical 
mountain  climates  have  not  as  yet  been  carefully 
studied.  Junghuhn  has  noted  an  improvement  in 
the  physical  condition  of  people  who  live  at  altitudes 
of  6000  to  6500  feet  in  Java;  in  Africa,  the  Zulus  and 
Hovas  have  been  instanced  as  furnishing  an  example 
of  the  strengthening  influence  of  mountain  climates, 
and  other  cases  are  cited  of  mountain  tribes  who  rob, 
or  rule  over,  lowland  tribes.  On  the  other  hand,  in 
Mexico,  Jourdanet  has  described  the  aneemic  condi- 
tion, poor  physical  development,  low  birth-rate,  and 
short  lives  of  the  inhabitants  of  the  plateau  of  Ana- 
huac,  and  Charnay  noted  the  fact  that  the  Indians 
who  brought  sulphur  from  Popocatepetl  fell  off  in 
bodily  vigour  at  an  early  age.  Prescott,  however,  in 
his  Conquest  of  Mexico,  noted  that  the  physical 
development  of  the  Tlascalans  on  the  plateau  was  bet- 
ter than  that  of  the  people  of  the  lowlands.  The  en- 
larged lung-capacity  of  the  inhabitants  of  the  lofty 


THE  LIFE  OF  MAN  IN  THE  TROPICS        269 

punas  on  the  west  coast  of  South  America  has  natu- 
rally been  attributed  to  the  effect  of  the  rarefied  at- 
mosphere. It  is  interesting  to  observe  that  it  often 
happens  that  plateau  and  mountain  peoples  sicken 
and  are  unable  to  work  when  taken  to  sea-level,  and 
the  same  thing  is  true  of  lowlanders  who  are  taken 
to  considerable  altitudes.  The  Aymara  Indians  of 
Peru,  when  taken  down  to  sea-level  by  the  Spaniards, 
could  not  stand  the  change.  Great  difficulty  has 
been  found,  as  pointed  out  by  Spence,  in  securing 
labourers  on  coffee  plantations  at  altitudes  of  4000 
to  6000  feet  in  South  America.  Labourers  from 
greater  altitudes  and  from  near  sea-level  alike  become 
ill  and  unfit  for  work.  Additional  examples  might  be 
cited. 

Special  mention  may  be  made  here  of  a  peculiar 
relation  between  climate  and  man  on  certain  lofty 
tropical  mountains,  which  are  snow-capped,  and 
which  furnish  a  supply  of  snow  or  ice  for  refrigerat- 
ing purposes  in  the  towns  below  them.  Thus  in 
Ecuador,  snow  is  carried  to  Quito  from  the  upper 
slopes  of  Pichincha;  to  Riobamba  and  Ambato  from 
the  slopes  of  Chimborazo.  Ambato  used  to  supply 
its  brewery  with  snow  from  the  same  mountain. 
Guayaquil  was  formerly  supplied  with  ice  in  the  same 
way.  In  Colombia,  Popayan,  in  the  department  of 
Cauca,  is  also  supplied  with  ice  and  snow  from 
neighbouring  mountains.  In  parts  of  Syria,  also, 
snow,  gathered  in  the  mountains,  is  packed  firmly 
in  pits  dug  in  the  ground,  and  covered  with  straw 


270  CLIMATE 

and  leaves.  It  is  later  sold.  In  Mexico,  snow  is 
carried  from  the  summit  of  Colima  to  the  towns  on 
the  hot  plains  below.  Howarth  notes  the  discovery 
of  an  "  ice  factory  "  in  one  of  the  highest  valleys  in 
Oajaca,  in  Mexico,  at  an  altitude  of  8000-9000  feet. 
In  this  case  the  active  nocturnal  cooling  by  radiation 
is  the  effective  climatic  factor  at  work.  "  The 
ground  was  covered  with  a  vast  number  of  shallow 
wooden  troughs,  which  are  filled  at  nightfall  with 
water  from  the  dividing  stream,  and  during  the  nights 
of  the  winter  months  this  becomes  covered  with  a  film 
of  ice  not  more  than  one-eighth  of  an  inch  thick.  In 
the  morning  this  is  removed  and  shovelled  into  holes 
in  the  ground,  and  covered  up  with  earth,  after  which 
it  consolidates  and  is  cut  out  in  blocks  and  sent  down 
by  mules,  where  there  seems  to  be  a  ready  market  at 
all  seasons."  On  the  high  veldt  the  Boers  keep  their 
provisions  by  letting  them  cool  outdoors  at  night. 
The  peculiarly  dry  climate  of  the  plateaus  of  the  west 
coast  of  South  America  is  due  to  the  leeward  posi- 
tion, west  of  the  Cordilleras.  The  Incas  preserved 
their  dead  by  allowing  them  to  mummify  naturally 
in  the  dry,  rare  atmosphere. 

The  construction  of  railroads  at  high  altitudes  in 
the  tropics,  as  on  the  west  coast  of  South  America, 
has  been  delayed  and  rendered  expensive  by  moun- 
tain sickness,  and  by  man's  decreased  efficiency  for 
work;  by  cloud-bursts,  flooded  rivers,  and  landslides. 
In  the  higher  passes  over  the  mountains,  diurnal 
winds  are  sometimes  met  with  of  such  velocity  that 


THE  LIFE  OF  MAN  IN  THE   TROPICS        271 

travelling  by  day  is  impossible  at  certain  seasons. 
Moritz  Wagner  has  described  the  down-cast  winds 
from  the  snowfields  near  Quito,  which  at  certain 
times  are  of  such  violence  as  entirely  to  interrupt 
travel  across  the  Chimborazo  passes.  Darwin  and 
many  others  have  noted  the  diurnal  variation  in  the 
height  of  water  in  rivers  fed  by  melting  snow.  Such 
streams  are  easiest  to  ford  in  the  early  morning, 
when  the  water  is  lowest. 


CHAPTER  IX 

THE  LIFE  OF  MAN  IN  THE  TEMPERATE  ZONES 

Climate  and  Man  in  the  Temperate  Zones:  General — Northward 
Movement  of  Civilisation  in  the  North  Temperate  Zone — 
Present-day  Migrations  within  the  Temperate  Zones — The 
Continents  and  the  Temperate  Zones — Differences  between 
Northerners  and  Southerners — Variety  of  Conditions  in  the 
Temperate  Zones:  Classification — Life  of  Man  in  the  Forests 
of  the  Temperate  Zones — Forest  Clearings — The  Steppes — 
Climates  and  Crops  in  the  Temperate  Zones — The  Des- 
erts— Mountains — Climate  and  Weather:  Some  Mental  Effects 
— Climate  and  Weather  and  Military  Operations — Railroads — 
Transportation  by  Water — Various  Effects  of  the  Weather. 

Climate  and  Man  in  the  Temperate  Zones:  Gen- 
eral. Intermediate  in  location,  in  mean  temperature, 
and  in  their  physiological  effects,  the  temperate 
zones,  whatever  was  the  condition  in  the  past,  are  to- 
day clearly  the  centre  of  the  world's  civilisation,  as 
they  have  also  been  the  scenes  of  the  most  important 
historical  developments  for  several  centuries.  From 
the  temperate  zones  have  come  the  explorers  and  ad- 
venturers of  the  past,  and  are  coming  the  exploiters 
and  colonisers  of  to-day.  In  the  occurrence  of  the 
temperate  zone  seasons  lies  much  of  the  secret — who 
can  say  how  much  of  it? — of  the  energy,  ambition, 

272 


LIFE   OF  MAN  IN  TEMPERATE  ZONES       273 

self-reliance,  industry,  thrift,  of  the  inhabitant  of  the 
temperate  zones.  Guyot  did  not  exaggerate  when 
he  wrote: 

In  the  temperate  zones  all  is  activity,  movement.  The 
alternations  of  heat  and  cold,  the  changes  of  the  sea- 
sons, a  fresher  and  more  bracing  air,  incite  man  to  a 
constant  struggle,  to  forethought,  to  the  vigorous  employ- 
ment of  all  his  faculties.  A  more  economical  Nature  yields 
nothing  except  to  the  sweat  of  his  brow;  every  gift  on  her 
part  is  a  recompense  for  effort  on  his.  .  .  .  Invited  to 
labour  by  everything  around  him,  he  soon  finds,  in  the  exer- 
cise of  all  his  faculties,  at  once  progress  and  well-being. 

The  monotonous  heat  of  the  tropics  and  the  con- 
tinued cold  of  the  polar  zones  are  both  depressing. 
Their  tendency  is  to  operate  against  man's  highest 
development.  The  seasonal  changes  of  the  temper- 
ate zones  stimulate  man  to  activity.  They  develop 
him  physically  and  mentally.  They  encourage  higher 
civilisation.  A  cold,  stormy  winter  necessitates  fore- 
thought in  the  preparation  of  clothing,  food,  and 
shelter  during  the  summer.  Carefully  planned, 
steady,  hard  labour  is  the  price  of  living  in  these 
zones.  Development  must  result  from  such  condi- 
tions. In  the  warm,  moist  tropics,  life  is  too  easy. 
In  the  cold  polar  zones  it  is  too  hard.  Temperate 
zone  man  can  bring  in  what  he  desires  of  polar  and 
tropical  products,  and  himself  raises  what  he  needs 
in  the  great  variety  of  climates  of  the  intermediate 
latitudes.  Near  the  poles  the  growing  season  is  too 
short.  In  the  moist  tropics  it  is  so  long  that  there  is 

18 


274  CLIMATE 


little  inducement  to  labour  at  any  special  time.  The 
regularity  and  the  need  of  outdoor  work  during  a 
part  of  the  year  are  important  factors  in  the  develop- 
ment of  man  in  the  temperate  zones.  Where  work  is 
a  universal  necessity,  labour  becomes  dignified,  well- 
paid,  intelligent,  independent. 

Behind  our  civilisation  there  lies  what  has  been  well 
called  a  "  climatic  discipline," — the  discipline  of  a 
cool  season  which  shall  refresh  and  stimulate,  both 
physically  and  mentally,  and  prevent  the  deadening 
effect  of  continued  heat.  On  the  other  hand,  a  very 
long  winter  is  about  as  unfavourable  asj^ery  long 
summer.  If  outdoor  work  is  seriously  interrupted, 
progress  is  retarded.  Buckle  based  certain  too  broad 
generalisations  on  this  consideration,  and  saw  in  it 
an  explanation  of  similar  national  characteristics 
among  peoples  whose  outdoor  work  is  interrupted  for 
the  same  length  of  time.  But  it  is  clear  that  the 
length  of  the  farming  season  is  a  large  factor  in  con- 
trolling the  return  from  the  soil,  the  kind  of  work 
done,  and  the  manner  of  doing  it.  It  is  not  sur- 
prising to  learn  that  the  difficulty  of  keeping  farm 
labourers  through  the  long  winter  has  in  the  past  been 
a  handicap  in  western  Canada,  and  that  it  was  urged 
against  the  abolition  of  slavery  in  Russia  that  it  would 
be  impossible,  without  some  form  of  compulsion,  to 
keep  farm-hands  through  the  winter. 

Northward  Movement  of  Civilisation  in  the  North 
Temperate  Zone.  The  gradual  migration  of  the 
centre  of  civilisation  away  from  the  tropics,  and  the 


LIFE  OF  MAN  IN  TEMPERATE  ZONES       275 

highest  development  of  the  human  race,  not  where 
life  is  easiest,  but  in  extra-tropical  latitudes,  are 
significant. 

"  Slowly  but  surely,"  as  Benjamin  Kidd  says  [Control  of 
the  Tropics,  51-52],  "we  see  the  seat  of  empire  and  au- 
thority moving  like  the  advancing  tide  northward.  The 
evolution  of  character  which  the  race  has  undergone  has 
been  northwards  from  the  tropics.  .  .  .  Underneath  all  the 
outward  national  quarrels  of  Europe  there  has  been  going 
on  for  centuries  what  is  really  a  struggle  between  what  we 
might  call  the  Latin  type  of  civilisation,  represented  by  the 
southern  races,  and  that  type  of  civilisation  which  has  been 
developed  in  northern  Europe." 

From  the  Mediterranean  region,  where  the  world's 
civilisation,  its  commerce,  and  its  power  were  long 
centred,  westward  through  Spain  and  Portugal,  the 
migration  continued  farther  and  farther  north  in 
Europe,  until  Holland  and  then  England  became  the 
dominant  power.  From  lands  of  more  genial  cli- 
mates to  lands  of  colder  and  longer  winters,  but  also 
of  the  most  active  and  energetic  races,  the  migration 
has  taken  place.  The  advance  of  Christianity,  from 
its  origin  in  the  subtropical  belt  of  Eurasia  into  higher 
latitudes,  has  been  pointed  to  as  another  illustration 
of  the  same  tendency.  Together  with  this  northward 
tendency  of  civilisation  there  has  run  through  the  past 
an  equatorward  movement,  already  noted  in  the  case 
of  the  tropics,  of  the  stronger  peoples  of  the  north 
toward  the  milder  and  more  genial  southern  latitudes, 
involving  historical  events  of  great  importance. 


276  CLIMATE 

Present-day  Migrations  within  the  Temperate 
Zones.  Within  the  north  temperate  zone  especially, 
and  also  across  from  the  north  to  the  south  temper- 
ate, vast,  peaceful  migrations  are  taking  place,  deter- 
mined largely  by  climatic  considerations.  From 
Europe  and  Asia  to  the  United  States  alone,  a  million 
people  a  year  are  now  migrating.  These  immigrants 
have  shown  marked  tendencies  to  settle  where  cli- 
mate, soil,  and  occupations  are  most  like  those  of  their 
old  homes,  although  the  fact  that  most  of  them  land 
at  one  port  on  the  eastern  seaboard,  the  concentra- 
tion of  industries  in  certain  sections,  and  other  con- 
trols, have  operated  very  effectively  to  counteract 
and  interfere  with  this  tendency.  Scandinavians, 
for  example,  have  gone  largely  into  the  north-west; 
and  in  the  future  the  southern  parts  of  the  United 
States  will  doubtless  have  a  large  Latin  popula- 
tion, chiefly  of  Italians  and  Spaniards,  who  will  there 
find  homes  and  occupations  in  climates  best  suited  to 
their  needs.  Canada  has  grown  slowly,  partly  on  ac- 
count of  the  repelling  effect  of  her  long,  cold  winters 
and  her  generally  severe  climate.  Of  late  years, 
however,  the  rapid  settlement  of  farming  lands  in  the 
United  States,  the  attraction  of  free,  or  cheap,  lands 
in  western  Canada,  and  the  success  which  has  been  at- 
tained in  raising  wheat  and  other  crops  during  the 
short  but  favourable  Canadian  summer,  have  com- 
bined to  induce  a  considerably  increased  immigration 
of  farmers  from  the  United  States,  and  of  Europeans, 
into  Canada.  This  migration  within  the  temperate 


LIFE  OF  MAN  IN   TEMPERATE  ZONES       277 

zone  is  peopling  Canada,  South  Africa,  and  Aus- 
tralia with  the  same  stock  that  occupies  the  home- 
land of  the  British  Isles.  Therefore  institutions  and 
government  essentially  similar  to  those  at  home  are 
possible  in  these  colonies  of  England  beyond  the  sea. 
The  case  is  very  different  in  tropical  climates,  as  has 
been  seen.  Russia  will  later  be  found  to  gain  great 
strength  from  the  fact  that  she  has  expanded  east- 
ward within  the  same  zone. 

In  Argentina,  the  climatic  control  of  migrations  is 
even  more  clearly  marked  than  in  the  United  States, 
the  Italians  tending  to  settle  towards  the  north,  where 
the  climate  is  most  like  their  own,  while  the  races 
from  northern  Europe  show  a  tendency  towards  the 
south. 

It  is  interesting  to  observe  how  immediately  con- 
trolled by  the  special  weather  conditions  of  even  one 
season  these  voluntary  migrations  may  be.  Years  of 
sufficient  rainfall  and  abundant  crops  in  the  United 
States  are  always  followed  by  a  larger  immigration. 
A  failure  of  crops  in  Europe,  whether  it  be  of  wheat 
in  one  country,  or  of  fruit  in  another,  or  of  potatoes  in 
another,  resulting  from  drought,  or  storms,  or  exces- 
sive rainfall,  always  promotes  a  larger  exodus  from 
the  country  concerned.  There  is,  furthermore,  a 
considerable  seasonal  migration  across  the  Atlantic. 
Thousands  of  Italians  come  to  the  United  States  in 
the  spring  to  work  during  the  warmer  months,  when 
farm  and  outdoor  labourers  are  in  demand,  and  re- 
turn to  the  milder  climate  of  Italy  for  the  winter. 


278  CLIMATE 

Similarly  there  is  a  seasonal  migration,  also  chiefly  of 
Italians,  to  Argentina  at  harvest  time.  The  possible 
effects  of  the  advancing  ice-sheet  of  the  glacial  period 
in  producing  forced  migrations  equatorward  may  be 
mentioned,  in  passing,  as  another  example  of  climatic 
controls  over  human  movements. 

There  is  also  an  interesting  tendency  westward, 
observable  not  only  in  the  westward  "  course  of  em- 
pire," but  in  the  advantages  enjoyed,  in  the  belt  of 
prevailing  westerly  winds,  by  those  who  live  in  the 
western  quarters  of  cities.  The  "  west  ends  "  are 
usually  the  most  fashionable  and  the  newest  sections 
of  these  cities,  while  the  quarters  to  leeward,  the 
"  east  sides  "  and  "  east  ends,"  are  inhabited  by  the 
poorer  classes.  Ratzel  points  out  that  among 
the  Arabs  of  Syria  the  tent  farthest  west  is  that  of 
the  sheik. 

The  Continents  and  the  Temperate  Zone.  Europe 
is  well  situated  climatically,  being  almost  altogether 
in  the  temperate  zone,  and  open  to  the  ocean  on  the 
west,  so  that  nearly  all  parts  of  it  are  wrell  watered. 

Asia  is  an  overgrown  continent.  Much  of  it  is  in 
the  temperate  zone,  it  is  true,  but  the  interior  is  so 
far  from  the  sea  that  the  climate  is  severe  and  the 
rainfall  very  deficient.  This  condition  of  hopeless 
aridity  is  depressing,  in  the  extreme,  and  this  region 
is  prevented  from  becoming  thickly  populated  or  im- 
portant on  that  account. 

Most  of  Africa  is  within  the  tropics.  Its  plateaus 
will  furnish  considerable  areas  not  wholly  unfavour- 


LIFE   OF  MAN  IN   TEMPERATE   ZONES       279 

able  for  white  settlement.  The  southern  part  of 
Africa  is  just  within  the  marginal  sub-tropical  belt 
of  the  south  temperate  zone.  The  same  is  true  of 
Australia. 

North  America  is  widest  in  the  temperate  zone, 
which  is  one  of  its  greatest  assets.  It  suffers  from  the 
extreme  cold  of  its  winters  in  the  north,  and  from  the 
rain-shadow  effect  of  its  western  mountains,  which 
gives  the  interior  basin  and  part  of  the  western  plains 
deficient  precipitation. 

South  America  is  widest  within  the  tropics.  Its 
west  coast  is  peculiar  in  having  the  tempering  in- 
fluence of  high  plateaus  in  the  interior  and  of  a  cool 
ocean  current  along  the  coast.  Its  southern  portion 
tapers  off  into  the  south  temperate  zone.  This  part 
of  South  America,  and  the  scattering  islands  of  the 
ocean  area  in  these  latitudes,  suffer  from  an  equable 
but  cheerless,  depressing,  and  inhospitable  climate. 
The  forlorn  natives  of  Tierra  del  Fuego,  most  inade- 
quately clothed  and  housed;  living  on  shell-fish  and 
other  sea-food;  with  the  poorest  kind  of  utensils  and 
implements;  nomadic  in  habits;  shifting  their  single 
fur  garment  from  side  to  side  according  to  the  wind 
direction — these  furnish  a  good  illustration  of  man's 
mastery  by  a  climate  which  Darwin  described  in  the 
following  words :  "  It  would  be  difficult  to  imagine  a 
scene  where  he  (man)  seemed  to  have  fewer  claims  or 
less  authority.  The  inanimate  works  of  nature- 
rock,  ice,  snow,  wind,  water — all  warring  with  each 
other,  yet  combined  against  man — here  reigned  in 


280  CLIMATE 

absolute  sovereignty."  The  Falkland  Islands,  by 
reason  of  their  "dull,  moist,  cool,  and  windy  climate, 
produce  nothing  but  a  few  poor  potatoes  and  some 
berries.  All  other  food,  excepting  mutton  and  beef, 
has  to  be  imported.  Very  different  is  the  life  of  man 
in  the  same  latitudes  of  the  continents  in  the  northern 
hemisphere,  where  a  more  severe  climate  has  given 
better  opportunity  for  man's  development. 

Differences  between  Northerners  and  Southerners. 
There  are  certain  broad,  distinguishing  charac- 
teristics of  man  in  the  temperate  and  tropical  zones, 
in  determining  which  it  is  reasonable  to  believe 
that  climate  has  played  a  part.  Similarly,  there 
has  been  a  natural  tendency  to  attribute  certain 
differences  between  northerners  and  southerners  in 
the  temperate  zones  to  a  difference  in  climate. 
There  is  an  opinion  that  the  former,  living  in 
a  duller,  harsher  climate,  with  long  and  dreary 
winters,  are  more  serious,  more  industrious,  more 
enterprising,  and  act  after  more  mature  delibera- 
tion, than  the  latter  who,  reflecting  their  brighter 
skies,  are  more  cheerful,  more  emotional,  more 
impulsive,  more  genial,  more  generous,  but  also 
less  energetic,  and  more  easy-going.  It  has  recently 
been  pointed  out  by  Professor  Jerome  Dowd  that 
labour  organisations  in  the  southern  United  States 
are  hampered  by  their  liability  to  hasty,  ill-advised 
action.  The  northerner  must  exercise  more  fore- 
thought, care,  industry,  and  prudence ;  he  has  to  work 
harder,  and  is  usually  better  paid  than  the  southerner. 


LIFE   OF  MAN  IN   TEMPERATE   ZONES       281 

These  national  differences  are  proverbial  between 
northern  and  southern  Germans,  French,  Spanish, 
Russians,  Italians,  Arabs,  and  other  peoples.  The 
influence  of  climate  has  likewise  been  traced  in  the 
sad,  even  pessimistic  tone  of  much  of  the  northern 
literature,  and  in  the  gravity  and  melancholy  of  mod- 
ern northern  music,  as  well  as  of  the  older  northern 
folk-songs. 

The  question  is  a  very  complex  one,  often  much 
complicated  by  actual  racial  differences  between  the 
northern  and  southern  people  of  the  same  country. 
Yet  even  racial  distinctions  are  more  or  less  directly 
traceable,  in  many  instances,  to  climate.  Thus  a  re- 
cent writer,  Gustave  Michaud  (The  Century,  March, 
1903),  has  told  us  that  the  Baltic  race 

is  probably  the  result  of  the  natural  selection  by  a  cold 
climate  over  emigrants  who  belonged  to  the  primitive  Medi- 
terranean race,  and  who  gradually  moved  northward.  Many 
of  their  mental  as  well  as  their  physical  characteristics  find 
an  explanation  in  that  hypothesis ;  those  individuals  who, 
through  lack  of  ingenuity,  foresight,  or  activity,  were  un- 
able to  meet  the  requirements  of  a  severe  winter,  perished 
generation  after  generation;  their  posterity  was  constantly 
decreased,  and  the  posterity  of  the  active,  energetic,  and 
thoughtful  was  thereby  relatively  increased. 

Sir  Archibald  Geikie,  in  his  Scottish  Reminiscences, 
has  emphasised  the  climatic  influence  in  producing 
the  grim  character  of  the  Scot  in  the  following 
words:  "  The  gloom  of  his  valleys  is  deepened  by  the 
canopy  of  cloud  which  for  so  large  a  portion  of  the 


282  CLIMATE 

year  rests  upon  the  mountain  ridges  and  cuts  off 
the  light  and  heat  of  the  sun.  Hence  his  harvests 
are  often  thrown  into  the  late  autumn,  and  in  many 
a  season  his  thin  and  scanty  crops  rot  on  the  ground, 
leaving  him  face  to  face  with  starvation  and  an  in- 
clement winter.  Under  these  adverse  circumstances 
he  could  hardly  fail  to  become  more  or  less  subdued 
and  grim." 

Draper  emphasised  the  important  historical  con- 
sequences of  the  difference  in  the  characteristics  of 
northerners  and  southerners  in  the  United  States, 
which  he  attributed  largely  to  climate,  and  which 
found  expression  in  the  Civil  War.  The  climate 
of  Virginia,  somewhat  more  genial  than  that  of  New 
England,  may  not  unreasonably  be  supposed  to  have 
made  its  mark  upon  the  early  settlers  in  the  former 
state,  while  the  Puritans  were  struggling  against  the 
harsher  forces  of  nature  in  the  north-east.  The 
Boers  in  Africa  have  developed  along  lines  different 
from  those  of  the  Dutch  in  the  United  States.  The 
climate,  soil,  and  crops  of  the  southern  states  made 
negro  labour  highly  desirable,  even  necessary,  and 
the  presence  of  the  negro  involved  some  form  of  com- 
pulsion— slavery. 

Variety  of  Conditions  in  the  Temperate  Zones: 
Classification.  The  temperate  zones  embrace  so  great 
a  variety  of  climates  that  it  is  not  practicable  to  con- 
sider the  relations  of  climate  and  man  according  to 
any  rigid  climatic  scheme.  It  is  simpler,  as  well  as 
more  logical,  to  consider  the  typical  examples  here 


LIFE  OF  MAN  IN  TEMPERATE  ZONES        283 

selected  according  to  the  broad  classification  of  for- 
ests, steppes,  and  deserts.  This  is  essentially  a  scheme 
which  depends  upon  rainfall,  and  is,  therefore,  a 
reasonable  one  for  adoption  by  those  who  approach 
the  subject  from  a  climatic  standpoint. 

Life  of  Man  in  the  Forests  of  the  Temperate 
Zones.  The  forests  of  the  temperate  zones  are 
chiefly  coniferous  on  highlands  and  in  colder  climates, 
and  deciduous  on  lowlands  and  in  lower  latitudes. 
They  are  found,  as  a  rule,  where  the  mean  summer 
temperature  is  over  50°,  where  the  rainfall  is  reason- 
ably heavy,  and  is  well  distributed,  and  where  soil 
and  other  factors  are  not  unfavourable.  Forests  are 
characteristic  at  the  present  time  of  the  rainy  west 
coasts  of  the  continents,  as  in  southern  Chile  and  on 
the  northern  Pacific  coast  of  North  America;  of 
much  of  the  interior  of  North  America  and  of  Siberia; 
of  the  Scandinavian  highlands.  On  the  north,  the 
great  forest  belts  merge  into  the  tundra  through  a 
/one  of  scattering  trees  and  stunted  bushes.  On  the 
south,  they  grade  into  the  open  steppe  country  of  the 
continental  interiors.  Much  of  the  temperate  zones, 
except  where  too  dry,  was  originally  forest-covered, 
but  the  trees  have  been  gradually  cleared  away  and 
an  open  country,  devoted  to  agriculture,  or  the  seat 
of  modern  manufacturing  and  industrial  settlements, 
has  taken  their  place.  The  southern  portions  of  the 
great  forest  belts,  because  of  their  more  favourable 
climates,  are  better  adapted  to  agriculture  than 
the  northern  portions,  and  are  therefore  first  attacked, 


284  CLIMATE 

as  is  now  the  case  in  Siberia.  The  more  severe  cli- 
mate of  the  latter,  and  their  greater  inaccessibility, 
will  help  to  preserve  them  from  destruction  for  farm- 
ing districts,  with  the  primitive  life  of  the  trapper 
and  woodsman  as  their  distinguishing  characteristic. 
The  temperate  zone  forests,  hampering  man's  move- 
ments, preventing  dense  population,  and  being  re- 
placed by  more  profitable  farming  country,  have 
thus  gradually  been  driven  back  from  the  lowlands 
onto  the  mountains  and  highlands  of  Europe,  where 
scattering  forests  alone  remain.  These  are  in  most 
cases  protected  by  government.  In  the  United 
States,  similar  clearing  has  been  going  on,  with  simi- 
lar consequences.  Many  of  the  forests  which  still 
remain  on  the  mountains  have  been  set  apart  as  na- 
tional forest  reserves,  in  order  that  they  may  serve 
as  regulators  of  water  supply  and  as  parks 
for  future  generations.  The  slow  spread  of  the 
white  population  in  the  United  States,  from  the 
originally  forested  eastern  section  where  it  so  long 
had  its  seat,  to  the  open  country  farther  west,  was 
certainly  in  part  due  to  the  great  difficulty  which 
the  early  settlers  experienced  in  clearing  away 
the  forests  which  they  found  on  the  Atlantic 
slope.  A  larger  population,  better  means  for  clear- 
ing the  forests,  and  improved  transportation,  later 
changed  this. 

The  foregoing  statements  must  not,  however,  lead 
us  to  jump  at  the  conclusion  that  all  open  areas  wrere 
once  forested,  and  thus  to  infer  that  a  supposed  de- 


LIFE  OF  MAN  Itf  TEMPERATE  ZONES       285 

forestation,  which  may  never  have  taken  place,  has 
produced  a  change  of  climate  which  has  not  been 
proved.  Many  such  cases  have  been  reported  for  the 
sub-tropical  belt  of  the  Mediterranean,  arid  for  South 
Africa,  but  sub-tropical  climates,  with  their  dry  sea- 
son and  light  rainfall,  are  riot  favourable  to  heavy 
forest  growth.  It  is  significant  that  the  ancient 
Greeks  imported  their  most  valuable  woods  from  the 
north. 

Before  the  forest  cover — the  natural  product  of 
soil  and  favourable  climate — is  cleared  away,  man  is 
chiefly  occupied  in  hunting  fur-bearing  animals  in 
the  colder  latitudes;  in  fishing,  and  in  lumbering. 
The  latter  occupation  is  greatly  facilitated  by  the 
winter  snows  in  northern  latitudes,  which  make  sledg- 
ing easy,  and  by  the  spring  freshets,  which  carry  the 
logs  down  to  the  saw-mills.  Where  there  is  no  snow, 
the  difficulty  and  expense  of  getting  out  the  timber 
are  usually  considerably  greater.  The  woodsman's 
life  is  primitive  and  hard,  and  retains  many  nomadic 
traces.  The  resort  to  u  the  woods  "  for  hunting  and 
fishing  by  a  good  many  people  from  the  north  tem- 
perate zone  for  a  part  of  the  year  brings  for  a  time  a 
relief  from  the  restraints  of  civilisation,  and  the  rest 
that  comes  from  a  return  to  more  primitive  condi- 
tions of  life.  There  is  a  considerable  seasonal  change 
of  occupation /among  the  lumbermen  of  the  northern 
United  States  and  of  Canada,  many  of  them  becom- 
ing farmers  or  sailors  in  summer.  Industries  which 
depend  upon  a  supply  of  lumber,  such  as  paper  and 


286  CLIMATE 

pulp  mills,  shipbuilding,  furniture,  carriage  and  bar- 
rel manufactories,  arid  the  like,  are  often  found  on  or 
near  the  streams  down  which  the  logs  are  floated* 
The  simple  log  hut  of  the  early  settler  in  the  Ameri- 
can forest  is  one  of  the  most  typical  forest  dwellings, 
which  are  naturally  built  of  wood.  The  Japanese 
houses  of  bamboo  and  wood  are  not  unsuitable  in  a 
region  of  tree-growth,  of  a  modified  continental  cli- 
mate, and  of  earthquakes.  Forest  fires  are  often 
very  destructive,  not  only  to  the  trees  themselves  but 
to  the  wooden  dwellings  in  the  forest. 

Fish  and  game  are  the  natural  food  of  forest  peo- 
ples, and  clothing  is  chiefly  made  of  fur  or  leather. 
Forest  products  are  brought  to  the  edge  of  the  forest 
for  sale  or  exchange.  Thus  the  trappers  in  North 
America  played  an  important  part  in  the  early  history 
of  that  continent.  Settlements,  which  were  originally 
trading  posts,  grew  up  along  the  streams,  and 
later  became  towns  and  cities.  Almost  all  the  large 
cities  of  the  north  Pacific  coast  of  the  United  States 
owe  their  prosperity  to  the  lumber  industry,  and  the 
same  is  true  of  other  cities  in  or  near  the  forested 
portions  of  the  country  east  of  the  Rocky 
Mountains. 

The  dense  Alaskan  coast  forests,  which  extend  far 
north  where  the  moisture,  even  without  high  tem- 
peratures, is  favourable  to  them,  have  to-day  certain 
noteworthy  effects  on  the  native  Indian  tribes  who 
live  along  their  borders.  The  density  of  vegetation 
and  the  difficulty  of  agriculture  force  them  to  turn 


LIFE   OF  MAN  IN   TEMPERATE  ZONES       287 

to  the  sea,  on  which  they  spend  most  of  their  time, 
on  which  they  travel,  and  from  which  they  obtain 
their  food.  They  become  expert  canoe-builders, 
sailors,  and  fishermen;  are  finely  developed  in  the 
upper  portions  of  their  bodies,  but  spend  so  much  of 
their  life  in  their  boats  that  they  dislike  walking  and 
are  poor  hunters  and  porters.  Their  food,  and  the 
material  for  some  of  their  utensils  and  implements, 
they  secure  from  the  sea.  They  wander  about  to  dif- 
ferent fishing-grounds,  living  a  more  or  less  nomadic 
life;  some  of  them  even  going  into  the  State  of 
Washington  in  harvest-time.  It  is  an  interesting 
fact  that  the  best  canoes  are  built  by  the  Indians  who 
live  in  the  most  stormy  locations,  and  these  same  peo- 
ple are  also  the  best  sailors.  On  the  coasts  of  south- 
ern Chile  the  dense  forests  have  kept  the  population 
close  to  the  sea;  have  made  clearing  for  farming  dif- 
ficult, and  have  resulted  in  making  lumbering,  hunt- 
ing, and  fishing  the  chief  occupations.  Darwin 
reported  of  this  region  that  the  constant  rains  keep 
everything  so  wet  that  to  clear  the  forest  by  fire  is 
almost  impossible. 

Forest  Clearings.  Man  gradually  makes  clearings 
in  the  virgin  forest,  and  then  cultivated  crops  take 
the  place  of  the  natural  tree-cover,  except  where  ex- 
tremely favourable  conditions  for  tree  growth,  or 
poor  soil,  or  steepness  of  slope,  make  forests  more 
profitable  than  agriculture.  At  present,  much  of  the 
population  of  the  civilised  wcrld  lives  in  such  clear- 
ings. Where  the  clearings  are  small,  as  in  parts  of 


288  CLIMATE 

Scandinavia,  the  life  is  simple,  combining  lumbering, 
hunting,  and  fishing  of  the  forest  with  agriculture. 
If  the  sea  is  near  by,  boat-building,  as  in  Norway, 
also  becomes  an  important  industry,  with  deep-sea 
fishing  and  sailing.  Simpler  industries,  like  wood- 
carving  and  match-making,  are  also  found.  Com- 
munities are  scattered,  and  are  largely  independent 
of  one  another.  Each  community  is  self-support- 
ing, and  each  individual  is  more  or  less  of  a  "  Jack-of- 
all-trades."  Isolated  clearings,  where  civilised  man 
is  making  the  first  inroad  into  the  primeval  temper- 
ate forest,  may  still  be  seen  in  several  parts  of  North 
America,  and  will  become  increasingly  common  in 
the  Siberian  forest  belt. 

With  the  destruction  of  the  forest  and  the  growth 
of  agriculture,  with  settled  places  of  abode  and  a 
reasonably  certain  food  supply  following  steady, 
careful,  and  intelligent  labour,  comes  the  gradual  ac- 
cumulation of  a  surplus,  and  the  increasing  diversity 
of  interests  and  occupations  which  characterise  the 
modern,  highly  civilised  community.  Here  we  find 
a  very  complex  life,  writh  industries  and  manufactures 
of  all  sorts;  where  raw  materials  and  supplies  are 
imported  from  other  lands  and  climates  and  exported 
to  them,  and  where  the  immediate  climatic  control 
often  becomes  difficult  to  see.  It  is  under  such  con- 
ditions that  civilised  man  lives  to-day,  using  the 
products  of  the  forest,  the  farm,  the  mine,  the  sea, 
the  lake,  the  river;  making  the  most  of  his  opportuni- 
ties; overcoming  more  and  more  the  disadvantages 


LIFE   OF  MAN  IN  TEMPERATE  ZONES       289 

of  his  immediate  surroundings.  It  remains  a  fact, 
nevertheless,  that  one  of  the  most  important  controls 
in  determining  the  location  of  modern  industries,  next 
to  nearness  to  materials  and  markets  and  water- 
power,  is  climate. 

The  Steppes.  In  the  intermediate  belts,  between 
the  heavier  rainfall  of  the  forested  districts  and  the 
deficient  rainfall  of  the  deserts,  come  the  grass-lands 
of  the  temperate  zones,  commonly  known  as  steppes 
("unwooded  tracts  in  middle  latitudes,  of  consider- 
able extent  and  covered  with  useful  vegetation"). 
These  are  found  where  the  rainfall  is  small  because 
of  distance  from  the  sea,  or  by  reason  of  the  rain- 
shadow  effect  of  enclosing  mountains,  and  over 
broad,  more  or  less  level  topographic  areas,  of  fairly 
uniform  climatic  conditions.  The  general  severity 
of  the  climate,  the  small  rainfall,  the  shortness  of 
the  growing  season,  and  other  factors,  such  as  high 
winds,  favour  grass  rather  than  tree  growth.  The 
central  Asiatic  plateau,  except  where  so  arid  as  to  be 
a  true  desert,  with  uniformity  of  climate  and  of  popu- 
lation, is  the  great  steppe  region  of  the  world. 
Southern  Siberia,  southern  Russia  and  Hungary, 
and  parts  of  Arabia,  Persia,  and  Asia  Minor  belong 
to  this  same  area.  The  Great  Plains  between  the 
Rocky  Mountains  and  the  100th  meridian  are  classed 
as  steppes,  as  are  the  grass-lands  of  eastern  temper- 
ate South  America.  The  Asiatic  steppe  is  extremely 
unfavourable,  so  far  as  occupation  and  development 
by  man  are  concerned.  At  the  centre  of  a  great 
19 


290  CLIMATE 

overgrown  continent,  with  the  trade  of  the  world 
naturally  passing  around  it,  largely  by  water,  rather 
than  across  it;  with  few  rivers  and  deficient  precipita- 
tion, the  effect  on  man,  whatever  may  have  been  the 
conditions  of  the  past,  is  such  as  to  depress,  retard, 
overcome  him.  Civilisation  there  lags  behind  that  in 
the  rainier  lands  of  the  temperate  zone.  The  grass- 
lands of  North  America,  it  may  be  noted,  have  the 
advantage  of  being  a  narrow  belt  between  two  well- 
watered  and  fertile  regions.  The  dry  season 
scorches  the  grass  and  dries  up  the  rivers;  the  spring 
rains  bring  out  the  carpet  of  grass  and  flowers. 
Winter  storms  and  cold  sweep  over  the  steppe,  often 
fatal  to  man  and  beast. 

The  primitive  inhabitants  of  the  Eurasian  steppe, 
like  the  Kirghiz,  Mongols,  Kurds,  are  nomads,  mov- 
ing about  during  the  summer  in  search  of  water  and 
pasturage  for  their  animals.  Their  migrations  often 
take  them  to  the  higher  country,  where  there  is  more 
chance  of  finding  water,  and  where  the  grass  is  bet- 
ter. A  dry  year  forces  migration  into  the  adjacent 
rainier  districts.  In  the  colder  months  the  people 
settle  down  in  more  permanent  abodes.  Thus  also 
we  find  the  inhabitants  of  the  Hungarian  plain 
townspeople  in  winter  and  semi-nomadic  farmers  in 
summer.  Professor  W.  M.  Davis  has  noted  the  use 
of  small  farm-houses  on  wheels  in  Bosnia,  which 
"  are  drawn  forward  on  the  plain  in  the  dry  season, 
so  as  to  stand  near  the  pasture  fields ;  and  back  again 
towards  the  higher  margin  in  the  wet  season."  The 


LIFE  OF  MAN  IN  TEMPERATE  ZONES       291 

driving  of  cattle  from  Argentina  across  the  moun- 
tains into  Chile  during  the  dry  season  is  another  in- 
stance of  seasonal  migration  in  search  of  pasturage 
in  grass-lands. 

The  primitive  steppe-dweller  depends  on  his  flocks 
and  herds  for  his  food  and  clothing,  and  for  his  tent- 
coverings  and  utensils.  From  their  wool,  or  hair,  he 
makes  his  cloth,  or  carpets.  The  summer  dwellings 
of  the  Asiatic  steppe-dweller  are  usually  felt  tents, 
adjustable,  portable,  skilfully  constructed.  These, 
with  simple  household  goods  made  principally  of 
leather,  at  once  the  most  available  and  most  useful 
material,  are  easily  transported  from  place  to  place. 
In  winter,  encampments  are  carefully  selected 
where  there  are  water  and  grass,  and  where  hay 
is  collected.  The  winter  dwellings  are  better  built, 
of  the  willows  or  reeds  found  along  the  streams,  and 
the  animals  are  sheltered  against  cold  and  storm. 
As  on  the  coastal  desert  of  South  America,  so  here, 
a  common  fuel  (in  winter)  is  the  dried  dung  of  ani- 
mals. Horses  are  a  precious  possession,  essential  to 
the  wandering  life  of  people  some  of  whom  call 
themselves  The  Horsemen  (Kazak).  The  trade  of 
the  Asiatic  steppe  is  carried  on  with  China  on  the 
one  side  and  Russia  on  the  other.  Hides  and  other 
products  obtained  from  the  flocks  and  herds  are  ex- 
changed for  tea,  flour,  opium,  clothing,  etc.  In- 
dependent, conservative,  and  proud,  the  natives 
retain  their  traditional  customs,  and  resist  the  en- 
croachments of  civilisation.  The  life  of  man  in 


292  CLIMATE 

steppe  and  in  tundra  has  many  points  of  resem- 
blance, but  the  steppe  is  the  more  favourable  to 
improvement- 

The  early  life  of  the  white  man  on  the  Great  Plains 
of  North  America  has  been  similar  in  many  ways  to 
that  on  the  Asiatic  steppes.  Immense  herds  of  cattle 
have  grazed  at  will  over  a  vast  extent  of  territory, 
driven  here  and  there  in  search  of  pasturage  and  wa- 
ter, and  tended  by  semi-nomadic  cowboys  spend- 
ing most  of  their  lives  in  the  saddle.  The  gradual 
destruction  of  the  natural  grass  forage  by  over-stock- 
ing, and  by  the  introduction  of  sheep,  has  not  in- 
frequently led  to  armed  conflicts  between  those  in 
charge  of  different  herds  of  cattle.  The  United 
States  has  also  illustrated  what  has  been  observable  in 
other  lands,  viz.,  the  conflict  between  the  divergent 
interests  of  those  who  want  grass-lands  for  agricul- 
ture and  those  who  want  them  for  grazing.  In 
North  America  the  conflict  was  not  waged  with 
bloodshed,  but  history  furnishes  examples  of  the  war- 
like encroachment  of  pastoral  nomads  into  the  peace- 
ful farming  communities  on  the  borders  of  the  steppe. 
China,  for  example,  was  invaded  by  steppe-dwellers, 
as  was  Europe  at  one  time;  even  to-day,  Kurds  and 
Armenians  are  struggling  in  a  similar  way.  In  the 
United  States,  the  facility  of  communication  and  the 
rapid  advance  of  population  from  the  east  have  led, 
in  recent  years,  to  a  considerable  change  in  the  use 
of  certain  portions  of  the  Great  Plains  steppe  region. 
After  an  almost  exclusive  use  of  these  plains  for  cat- 


LIFE   OF  MAN  IN   TEMPERATE   ZONES       293 

tie,  farming  without  irrigation  was  tried  over  their 
central  portion  in  the  latter  part  of  the  decade  1880- 
1890,  during  and  closely  following  a  series  of  years 
with  a  rainfall  somewhat  above  the  average.  The 
experiment  proved  to  be  a  failure  when  a  series  of 
drier  years  followed.  Since  then,  local  irrigation  by 
means  of  wind-mills  has  been  introduced  to  a  con- 
siderable extent,  and  diversified  farming  under  irri- 
gation, with  cattle-raising  on  a  much  smaller  scale 
than  formerly,  has  been  found  to  be  a  far  more  profit- 
able undertaking  than  farming  on  a  large  scale  with- 
out irrigation.  The  cattle  are  fed,  when  necessary, 
with  alfalfa  or  other  forage  raised  for  that  purpose; 
are  bred  under  supervision,  and  are  protected  against 
the  severe  winter  storms  and  cold.  The  climatic 
limitations  of  the  Great  Plains  are  now  clearly  re- 
cognised. By  far  the  greater  portion  must  forever 
remain  pastoral,  but  where  irrigation  can  be  prac- 
tised, farming  and  cattle-raising  together  are  more 
profitable  than  either  alone.  Irrigation,  together 
with  the  proper  preparation  of  the  soil  and  the  plant- 
ing of  crops  suited  to  the  climate,  has  worked  a  com- 
plete change  in  the  appearance  and  in  the  economic 
value  of  many  parts  of  the  Great  Plains.  The  large 
modern  cattle  ranch  in  the  western  United  States  is 
very  different  from  the  wandering  cattle  herd  of  a 
few  years  ago.  There  are  summer  and  winter 
ranges  for  the  stock,  the  winter  range  being  sheltered 
as  much  as  possible.  On  a  well-equipped  ranch,  a 
barometer  is  watched  as  carefully  as  on  board  ship. 


294  CLIMATE 

When  a  storm  is  expected,  the  sheep  or  cattle  are 
brought  to  shelter  if  possible,  or  if  not,  are  driven  to 
windward,  so  that  they  will  be  driven  home  by  the 
storm.  In  Australia  the  grass-lands  have  been  oc- 
cupied by  British  sheep-owners,  employing  native 
stockmen,  and  the  conditions  of  life  are  much  like 
those  of  the  ranchmen  on  the  Plains  of  North 
America. 

Obviously,  wherever  irrigation  is  possible,  steppes 
become  more  valuable  for  farming  than  for  grazing. 
There  is  a  limit  to  the  water  supply,  whether  that 
come  from  rivers  or  from  underground,  and  an  in- 
creasing population,  with  increasing  demands  for 
water,  must  in  time  reach  the  limits  of  the  supply. 
In  many  of  the  western  states  of  the  American 
Union,  where  with  increasing  population  the  need  of 
irrigation  has  been  felt  more  and  more,  much  litiga- 
tion has  arisen  concerning  the  right  to  water.  The 
difficulties  have  come  in  great  measure  from  the  fact 
that  the  laws  were  imported  from  rainier  regions, 
where  irrigation  was  unnecessary.  On  the  Asiatic 
steppes,  Russian  influences  are  encouraging  irriga- 
tion and  agriculture.  As  a  rule,  the  steppes  of  the 
temperate  zone  have  been  cultivated  where  settled 
by  people  who  had  formerly  been  farmers  in  more 
humid  regions. 

The  wide  expanse  of  the  steppes,  with  their  un- 
obstructed surface,  situated  as  they  usually  are  in 
the  extreme  climates  of  the  continental  interiors,  ex- 
poses them  to  sudden  temperature  changes.  The  far- 


LIFE   OF  MAN  IN  TEMPERATE  ZONES       295 

reaching  sweep  of  cold  storm  winds  from  higher  lati- 
tudes, such  as  the  cold  norther  or  blizzard  of  North 
America  and  the  buran  of  Siberia,  may  destroy 
thousands  of  cattle  in  a  few  hours  and  not  infre- 
quently human  lives  as  well.  Depressing  hot  winds 
from  lower  latitudes,  which  carry  high  temperatures 
far  poleward,  sometimes  injure  crops  by  their  heat 
and  dryness.  In  dry  times,  fires  once  started  have 
a  free  sweep  over  the  open  steppe  country. 

Climates  and  Crops  in  the  Temperate  Zones. 
The  variety  of  climates  found  over  the  temperate 
zones,  especially  in  the  northern  heimsphere,  is  very 
large,  ranging  from  the  modified  marine  climate  on 
the  west  coasts  to  the  extreme  continental  of  the  in- 
teriors and  the  modified  continental  on  the  east 
coasts,  and  also  varying  greatly  with  latitude.  No 
such  simple  discussion  according  to  climatic  sub- 
divisions is  possible  as  in  the  case  of  the  tropics. 
Forests  are  found  on  the  rainy  west  coasts  and  also 
in  the  interiors.  Agriculture  is  practised  where  the 
forest  has  been  cleared,  and  also  on  the  steppes  and 
even  in  the  deserts,  wherever  irrigation  is  possible. 
These  variations  in  climate  from  east  to  west  and 
north  to  south  across  a  continent,  are  such  as  to 
necessitate  great  differences  in  the  season  and 
methods  of  agriculture,  and  in  the  crops  that  are 
grown. 

In  the  sub-tropical  belts,  favoured  as  they  are  in 
many  ways  as  to  climate,  man  fights  against  frost  in 
California;  protects  his  crops  by  walls  or  hedges 


296  CLIMATE 

against  high  winds,  as  in  the  Azores,  in  Malta,  and 
in  southern  France;  manufactures  artificial  ice  in 
Palestine ;  retards  the  ripening  of  his  fruit  under  the 
spring  sun  by  screening  it.  The  latter  is  an  interest- 
ing phase  of  man's  effort  to  make  the  most  of  his 
climate,  regulating  it  so  far  as  may  be  possible.  In 
parts  of  Italy  it  is  customary  to  cover  the  lemons 
with  screens  of  cloth  or  rushes,  so  that  they  may  not 
ripen  until  the  summer  demand  is  at  its  height  in 
England  and  America,  and  prices  are  good.  The 
equable  climate  of  the  Pacific  coast  of  the  United 
States  makes  it  possible  to  keep  farm  animals  out- 
doors most,  or  even  all,  of  the  year,  thus  saving  the 
expense  of  barns  and  stables  necessary  in  more  rigor- 
ous climates.  In  summer  on  this  coast,  advantage  is 
taken  of  the  dry  season  to  leave  wheat  out  in  sacks, 
sometimes  for  weeks  at  a  time,  without  much  fear  of 
damage  by  rain.  This  is  a  great  convenience  for  the 
farmer.  Raisins  are  usually  dried  outdoors,  although 
some  of  the  larger  growers  are  now  introducing  dry- 
ing houses.  The  damage  done  by  one  rain  is  so  great 
when  raisins  are  partially  dry,  that  the  field  labourers 
at  such  critical  times,  when  rain  is  forecasted,  insist 
on  being  paid  extra  high  wages  to  bring  in  the  fruit. 
The  kind  of  agricultural  machinery  depends  largely 
upon  conditions  of  climate  and  crops.  The  com- 
bined harvester  and  thresher  used  in  California  could 
not  be  successfully  employed  under  other  conditions 
of  dryness  and  ripeness  of  the  grain.  The  use  of  this 
machine  is  much  restricted  farther  north,  in  Oregon 


LIFE  OF  MAN  IN  TEMPERATE  ZONES        297 

and  Washington.  It  may  here  be  noted,  in  passing, 
that  in  Norway  agricultural  machinery  has  been  well 
received  on  account  of  the  shortness  of  the  summer 
and  the  need  of  accomplishing  outdoor  work  quickly. 
Cereals  are  a  winter  crop  in  the  regions  of  winter 
rains,  and  many  fruits  can  be  very  successfully 
grown,  such  as  lemons,  figs,  olives,  oranges,  etc.  The 
sub-tropical  vine-growing  districts  of  Italy,  Spain, 
southern  France,  California,  southern  Australia,  and 
Cape  Colony  are  natural  centres  for  the  wine  industry. 

The  great  cereal  lands  of  the  world  are  found  in 
the  continental  interiors,  in  the  regions  of  summer 
rains,  where  the  precipitation  is  sufficient.  Roughly, 
between  latitudes  40°  and  52°,  other  conditions  be- 
ing favourable,  we  find  the  principal  wheat  belt;  but 
wheat  is  cultivated  much  farther  north,  for  example 
in  Asia,  and  also  farther  south  than  the  above  limits. 
Barley  grows  over  a  much  wider  belt,  both  poleward 
and  equatorward ;  oats  grow  north  of  wheat,  and  corn 
grows  south  of  it.  In  the  higher  latitudes,  with 
shorter  summers,  it  is  more  and  more  difficult  for 
cereals  to  ripen.  All  over  the  cleared  farm-lands  and 
cultivated  steppes  of  the  temperate  zone,  droughts, 
or  excessive  rains,  or  frosts,  or  other  harmful  condi- 
tions are  always  to  be  feared.  On  the  whole,  the 
struggle  against  adverse  conditions  of  climate,  and 
weather,  and  soil,  is  so  hard  that  it  constantly  de- 
mands man's  best  energies,  his  best  methods,  his  best 
implements. 

Climate  has,  in  a  large  way,  set  apart  certain  great 


298  CLIMATE 

areas  where  agriculture  may  be  best  carried  on. 
Similarly,  it  has  determined  that  one  area  shall  be 
adapted  for  grazing  and  another  for  forests.  For- 
ests will  always  grow  chiefly  in  the  rainier  regions, 
because,  although  trees  can  be  made  to  grow,  by  care- 
ful selection  and  proper  care,  over  a  good  deal  of 
steppe  country,  they  will  always  grow  better,  and 
faster,  and  more  cheaply,  where  the  rainfall  is  heavier. 
A  map  of  the  products  of  any  country,  in  crops,  or 
cattle,  or  forests,  will  show,  when  compared  with  a 
rainfall  map,  the  broad,  general  relations  which  are 
here  referred  to.  There  is,  it  may  be  noted,  often  an 
intimate  connection  between  a  product  of  one  sort 
and  one  of  another  sort,  as,  for  example,  in  the  case 
of  hogs  in  the  United  States,  which  are  raised  in 
largest  numbers  in  the  region  which  produces  the 
most  corn,  on  which  the  hogs  are  fed.  The  climatic 
control  of  occupations  is  beautifully  illustrated  in 
Chile.  In  the  rainy  south,  the  forests,  with  lumber- 
ing and  fishing;  in  the  arid  north,  the  deserts,  which 
would  be  uninhabited  were  it  not  for  the  nitrate  and 
other  mineral  deposits  which  have  given  the  region  an 
extraordinary  value;  in  the  central  portion,  with  a 
climate  neither  too  wet  nor  too  dry  for  agriculture, 
we  have  the  great  farming,  cereal,  and  stock-raising 
districts. 

The  Deserts.  In  the  continental  interiors,  where 
the  distance  from  the  ocean  is  great  and  the  enclosure 
by  surrounding  mountains  is  effective  in  intercepting 
the  moisture  brought  by  the  winds,  grass-land  is 


LIFE  OF  MAN  IN  TEMPERATE  ZONES      299 

replaced  by  sparser  and  sparser  vegetation;  steppe 
merges  into  desert;  population  decreases  more  and 
more.  Such  arid  regions  are  found  in  the  deserts 
of  south-eastern  California,  Arizona,  and  New  Mex- 
ico; in  northern  Mexico;  in  the  interior  of  the  great 
overgrown  continent  of  Asia.  These  deserts  are 
the  extreme  product  of  continental  climate.  With 
moderate  or  cold  winters  and  hot  summers,  the  life  of 
man  in  them  is  controlled  in  much  the  same  way  as 
in  the  deserts  of  the  tropics. 

No  more  striking  illustration  of  this  control  over 
the  primitive  desert-dwellers  of  the  temperate  zone 
has  been  given  than  in  the  study  made  by  McGee  of 
the  Papago  Indian  tribes  of  southern  Arizona.  "  The 
Papago  prefers  to  live  where  other  people  famish; 
he  is  able  to  do  so  by  reason  of  his  remarkable  adjust- 
ment of  his  habits,  his  food  and  raiment,  his  indus- 
tries, his  social  organisation,  to  a  peculiar  assemblage 
of  conditions."  These  people  can  go  long  without 
food  and  water;  in  emergencies  they  secure  water 
from  the  barrel  cactus  (biznaga)  *  :  they  chase  rain- 
storms for  miles  across  the  desert,  and  plant  wherever 
water  or  damp  soil  is  found;  their  houses,  built  of 
mesquite  saplings,  protected  against  the  ravages  of 
cattle  by  thorns,  or  of  adobe,  are  located  near  damp 
soil,  or  a  water  supply.  The  Papago's  life  is  nomadic 
for  much  of  the  year  because  he  migrates  in  search  of 
the  means  of  subsistence,  of  which,  as  McGee  puts  it, 

1  A  good  illustration  may  be  found  in  PI.  xviii  of  the  "  Desert 
Botanical  Laboratory  of  the  Carnegie  Institution,"   1903. 


300  CLIMATE 

"the  first,  and  the  second,  and  the  third  are  water, 
water,  WATER,  to  alleviate  his  own  thirst  in  the  sun- 
parched  deserts,  water  to  sustain  his  horses  and  burros 
and  kine,  water  to  vivify  the  plants  of  which  man  and 
his  creatures  eat."  The  seasons  of  planting  and  of 
harvest  depend  on  storms,  come  when  these  may; 
when  the  local  water-supply  fails,  water  is  carried 
long  distances  on  burros,  or  on  the  head;  the  springs 
are  protected  by  a  corral  or  stockade  made  of  cactus, 
and  even  of  the  dried  carcasses  of  bulls  killed  in  the 
battle  for  water;  only  the  simplest  arts  of  pottery- 
making  are  practised.  All  this  shows  a  climatic 
control  of  which  no  better  illustration  can  be  found 
anywhere  in  the  world.  The  thick  adobe  walls  of  the 
Indian  dwellings  of  the  south-western  United  States 
in  general  are  well  adapted  for  keeping  the  inside 
temperature  equable,  in  spite  of  the  large  diurnal 
ranges  outside.  The  Pueblo  Indians  show  the  in- 
fluence of  climate  in  their  use  of  stone,  and  in  the 
absence  of  wood  in  their  buildings  and  utensils.  Heat 
and  cold  split  the  rocks  of  their  mesas  and  furnish 
material  for  building.  The  reckoning  of  a  man's 
wealth  according  to  the  number  of  horses  in  his  pos- 
session; the  open  and  easily-transported  huts  of  the 
Navahoes,  which  furnish  sufficient  protection  against 
the  heat  and  the  wind  of  the  hotter  months,  with  more 
permanent  winter  houses  of  adobe,  better  fitted  as  a 
protection  against  the  severe  weather  of  the  colder 
season;  the  rain-dances  and  rain-gods  of  the  south- 
western United  States, — all  this  is  but  a  repetition  of 


LIFE   OF   MAN   IN   TEMPERATE   ZONES      301 

what  is  found  among  the  native  tribes  of  the  hot 
tropical  desert.  It  has  been  well  said  by  one 
writer  that  "  the  whole  religion  of  the  south-west 
may  be  summed  up  in  a  single  phrase — a  prayer  for 


rain." 


In  the  arid  interior  of  Asia  we  see  the  same  no- 
madic life,  the  same  difficulty  of  travel,  the  same  semi- 
pastoral,  semi-industrial  population  along  the  borders 
or  in  the  oases  of  the  desert,  as  in  the  tropics.  But  in 
the  temperate  zone  deserts  there  comes  always  the 
greater  need  of  protection  against  more  severe  cold. 
It  has  been  believed  by  many  writers  that  a  progres- 
sive desiccation  in  central  Asia  drove  the  inhabitants 
out  onto  the  lowlands,  and  was  followed  by  the 
Asiatic  invasion  of  Europe;  but  there  are  not  want- 
ing those  who  do  not  believe  such  desiccation  proved, 
and  who  doubt,  as  H.  J.  Mackinder  has  said,  whether 
these  changes,  even  if  proved,  have  "  in  historical 
times  vitally  altered  the  human  environment." 

In  time,  civilised  man  will  make  use  of  every  avail- 
able drop  of  water  which  is  supplied  in  these  arid  re- 
gions, whether  by  streams,  or  in  the  form  of  rain,  or 
from  underground,  and  the  irrigated  desert  will  de- 
velop in  man  those  qualities  of  cooperation  which  have 
been  conspicuous  in  the  irrigated  communities  of 
Peru,  among  the  Indians  of  the  south-western  United 
States,  in  Africa  and  in  Asia,  in  Utah  and  in  Cali- 
fornia. Where  every  drop  of  water  has  a  money 
value,  there  results  a  unification  of  interests  in  the 
common  water  supply  which  is  as  striking  as  it  is 


302  CLIMATE 

interesting.  But  there  is  a  limit  to  the  population 
whose  needs  can  be  supplied  in  these  deserts,  even 
when  every  available  water  supply  is  drawn  upon; 
and  the  temperate  deserts,  like  those  of  the  tropics, 
must  always  remain  sparsely  populated,  as  a  whole, 
with  their  inhabitants  collected  here  and  there  around 
oases,  or  in  the  larger,  modern,  irrigated  areas.  The 
immense  public  irrigation  works  recently  completed, 
or  now  being  carried  out  by  the  United  States  gov- 
ernment, furnish  striking  illustrations  of  the  effective 
use  which  civilised  man  now  makes  of  water  in  an 
arid  region,  while  the  Mormon  irrigation,  practised 
in  Utah,  still  remains  a  model  of  what  can  be  accom- 
plished by  individuals  working  in  harmony. 

A  typical  desert  industry  is  the  harvesting  of  salt, 
as  from  Great  Salt  Lake  in  Utah,  at  Salton  in  the 
California  desert,  in  Turkestan,  Patagonia,  and 
China.  In  the  last-named  country  salt  was  formerly 
used  as  money,  the  salt  industry  being  a  government 
monopoly,  protected  by  a  prohibition  of  the  importa- 
tion of  foreign  salt.  In  Chinese  Turkestan  blocks 
of  rock  salt  are  sometimes  used  in  building  walls,  and 
huts  built  of  rock  salt  have  also  been  reported.  The 
difficulty  of  securing  wrater  in  the  temperate  deserts 
is  often  serious.  Baku  is  to-day  supplied  in  part 
with  wrater  obtained  by  distilling  the  brackish  waters 
of  the  Caspian  Sea. 

Railroad  construction  and  operation  in  the  tem- 
perate deserts,  e.  g.,  in  Arizona  and  south-eastern 
California,  or  on  the  new  trans-Caspian  railroad  in 


LIFE   OF  MAN  IN  TEMPERATE   ZONES       303 

Asia,  and  on  the  projected  trans- Australian  railroad, 
have  to  contend  with  difficulties  similar  to  those  in  the 
tropical  deserts,  to  which  reference  has  already  been 
made.  A  curious  effect  of  sand-blasting  is  noted 
from  the  California  desert,  where  the  telegraph  poles 
along  the  railroad  are  so  worn  near  their  bases  by  the 
blowing  sand  that  they  have  to  be  protected  by 
piles  of  stones.  The  southern  trans-continental  rail- 
roads of  the  United  States,  which  traverse  the  hottest 
and  dustiest  part  of  the  interior  desert,  lose  much 
travel  in  summer  because  passengers  prefer  the  more 
northerly,  cooler,  and  less  dusty  journey. 

Mountains.  The  mountains  of  the  temperate  zones 
are  often  forest-covered  on  their  upper  slopes,  with 
pasture  lands  farther  down,  and  below  these,  the 
lower  slopes  are  used  for  agriculture.  The  variety 
of  occupations  within  a  restricted  area  is  thus  consid- 
erable, e.  g.3  lumbering,  forest  industries,  and  hunting 
above;  farming  and  fruit-growing  below.  Moun- 
tains which  rise  from  steppes  or  deserts  have  the  char- 
acter of  oases,  or  islands.  The  general  conditions 
of  climate  and  of  life  on  mountains  are  so  different 
from  those  on  lowlands  that  it  is  not  surprising  to 
note  the  differences,  often  observed,  between  moun- 
tain and  lowland  peoples.  The  decreasing  mean  tem- 
perature, the  inaccessibility,  the  smaller  amount  of 
land  available  for  profitable  use  (except  in  the  case  of 
mines),  and  the  decrease  in  plant  and  animal  life  for 
food,  suffice  to  set  a  limit  of  height  to  the  habitability 
of  these  mountains  by  man.  Human  settlements,  as 


304  CLIMATE 

a  whole,  therefore  decrease  in  number  and  impor- 
tance with  increasing  altitude,  except  where  mineral 
wealth  or  forests  are  an  attraction. 

The  successive  vertical  zones  or  belts  of  vegetation 
vary  much  in  altitude  above  sea-level,  according  to 
the  slope  on  which  the  plants  grow,  the  warmer 
southern  slopes  (in  the  northern  hemisphere)  giving 
vegetation  more  favourable  conditions  at  a  greater 
altitude  than  the  northern.  A  similar  effect  of 
favourable  exposure  is  commonly  seen  in  the  dis- 
tribution of  population  in  mountainous  districts. 
Human  settlements  are  usually  found  at  greater  ele- 
vations on  the  sunnier  slopes,  where  the  conditions  for 
agriculture  and  for  grazing  are  most  favourable, 
but  temporary  lumbering  or  mining  operations  may 
locally  induce  higher  settlements  on  the  shady  slopes, 
and  more  favourable  rainfall  on  the  latter  may  also 
bring  about  a  departure  from  the  general  rule.  The 
average  upper  limit  of  settlements  in  the  Alps  coin- 
cides fairly  well  with  the  upper  limit  of  grain.  It  is 
reported  that  in  the  Oetz  Valley,  in  the  Alps,  consid- 
erably more  than  75  per  cent,  of  the  population  live 
on  the  sunny  side  of  the  valley.  Lugeon's  study  of 
the  principal  valley  of  the  canton  of  Valais,  between 
Martigny  and  the  Rhone  glacier,  has  brought  out 
similar  interesting  facts.  In  a  certain  part  of  this 
district,  the  villages,  with  but  one  or  two  exceptions, 
are  on  the  sunny  side.  In  fact,  a  certain  distinction 
of  classes  results  from  this  difference.  There  is  de- 
veloped an  aristocracy  of  the  sun,  so  to  speak.  The 


LIFE   OF  MAN  IN  TEMPERATE  ZONES       305 

people  on  the  sunny  side  are,  on  the  whole,  more  pros- 
perous and  better  educated,  and  look  with  some  con- 
tempt upon  the  people  on  the  shady  side.  The 
marked  avoidance  of  the  lower  parts  of  valleys  in  the 
Alps,  and  in  other  temperate  mountain  regions,  and 
the  building  of  houses  on  the  mountain  slopes  or  the 
hill-tops,  depend  upon  the  frequent  occurrence  of 
inversions  of  temperature.  Lowl  has  pointed  out 
that  in  parts  of  the  Alps,  terraces,  fan-cones,  and 
other  topographic  forms  elevated  somewhat  above 
the  valley  floors,  are  thus  sought  out  as  locations  for 
houses. 

The  value  of  land  is  obviously  determined  largely 
by  its  position  with  reference  to  slope,  exposure,  and 
liability  to  frost  occurrence.  Southern  slopes  (in 
the  northern  hemisphere)  are  usually  more  desirable 
as  well  as  more  expensive,  and  many  examples  might 
be  given  of  the  difference  in  value  of  land  which 
is  more  exposed  to  frost  and  of  that  which  is  less 
exposed.  California  furnishes  many  excellent  ex- 
amples. A  grain  ranch  lying  in  a  frosty  pocket  may 
there  be  next  to  land  which  is  practically  frost-free. 
The  latter  is  worth  two  hundred  or  more  times  as 
much  per  acre  when  well  established  in  oranges.  The 
kind  of  crop  which  can  be  grown,  and  hence  the 
financial  return,  also  depends  largely  upon  exposure 
to  sunshine  and  frost,  protection  against  destructive 
winds,  and  the  like,  as  well  as  upon  soil. 

It  is  a  characteristic  habit  in  many  parts  of  the 
temperate  zones  to  drive  cattle  up  onto  the  higher 


306  CLIMATE 

slopes  of  the  mountains  for  pasturage  in  the  summer 
months,  whereas,  on  the  approach  of  the  winter,  they 
are  brought  back  to  the  permanent  settlements  be- 
low. Examples  are  found,  among  other  places,  in 
Switzerland,  where  the  cattle  and  goats,  with  their 
herders  and  shepherds,  spend  the  summer  far  up  on 
the  alp;  in  Sweden  and  Norway;  in  south-eastern 
France;  on  the  Balkan  peninsula;  among  certain  In- 
dian tribes  and  also  on  some  of  the  great  cattle  ranches 
of  the  United  States ;  in  much  of  the  plateau  country 
of  Asia,  as  on  the  Pamir,  and  in  parts  of  Armenia, 
the  Thian  Shan,  and  the  central  Himalayas ;  in  north- 
ern Africa,  and  in  the  Urals.  The  modern  develop- 
ment of  summer  resorts  in  mountains  is  but  another 
manifestation  of  this  seasonal  control  of  migrations 
by  the  climatic  conditions  resulting  from  the  presence 
of  mountains.  Special  cases  of  a  peculiar  kind  are 
found  in  the  Sary-Tur  and  Thian  Shan  mountains, 
among  the  Boginzes  and  the  Kirghiz,  who  in  winter 
drive  their  horses  and  herds  up  above  the  level  of  the 
winter  clouds  and  snows  to  the  upper  pastures,  which 
are  well  watered  by  the  summer  rains,  and  furnish 
abundant  grass  for  fodder.  Again,  in  Sistan,  Ells- 
worth Huntington  reports  an  occasional  migration 
down  from  the  relatively  cool  mountains  during  a 
dry  season,  and  across  the  desert  to  the  lake  waters 
beyond.  But  these  are  exceptions  to  the  general 
rule  of  upward  migrations  in  summer. 

The  forests  above  the  grass  zone  are  frequently 
the  last  resort  of  wild  animals  which  have  retreated 


LIFE   OF  MAN  IN   TEMPERATE   ZONES  .     307 

from  the  lower  slopes,  and  hunting  expeditions  in 
search  of  this  game  are  often  made. 

Mountain  peoples  have  special  conditions  to  meet. 
Their  dwellings  are  usually  better  built  and  furnish 
better  protection  than  is  the  case  on  the  lowlands.  In 
some  cases  the  people  live  almost  or  quite  under- 
ground, in  order  to  secure  the  maximum  protection 
against  cold,  or  heat,  or  high  winds.  In  Kashmir 
some  of  the  natives  carry  about,  under  their  loose 
clothing,  earthenware  pots  filled  with  live  coals,  to 
keep  them  warm.  Severe  winters  on  mountains,  with 
little  or  no  possibility  of  doing  outdoor  work,  pro- 
mote home  industries.  Foehn  or  chinook  winds  lo- 
cally favour  the  raising  of  special  crops  or  fruits; 
melt  the  snow  rapidly,  so  that  cattle  may  find  susten- 
ance through  the  winter;  or  necessitate  strict  regula- 
tions against  fires,  as  in  parts  of  Switzerland.  The 
bora  interferes  with  shipping  along  the  eastern  shore 
of  the  Adriatic.  Mountain  and  valley  winds  some- 
times locally  attain  such  violence  as  to  make  travel  or 
habitability  difficult  or  impossible. 

A  peculiar  custom  which  prevails  among  certain 
native  tribes  of  the  Himalayas,  and  which  is  an 
interesting  result  of  climate,  has  been  reported 
by  Ellsworth  Huntington  (in  manuscript).  Certain 
Kashmiris,  who  live  in  the  Himalayas  between  Kash- 
mir and  Ladakh,  at  an  altitude  of  about  10,500  feet, 
spread  earth  on  the  snow  in  order  to  make  the  snow 
melt  more  quickly. 

"  Those  whom  I  saw,"  reports  Huntington,  "  were  Kash- 


308  CLIMATE 

miris  who  had  come  to  the  country  within  a  generation  or 
two,  and  had  learned  the  practice  from  the  long-settled 
Ladakhi  or  Tibetan  inhabitants.  The  snow,  April  11,  1905, 
was  unusually  deep,  about  10  feet,  and  was  not  expected  to 
disappear  for  nearly  two  months,  some  two  weeks  later  than 
usual.  In  the  drier  region  of  Ladakh,  nearly  to  the  east, 
the  practice  is  followed  by  people  living  as  high  as  14,000 
feet.  Sometimes  a  snowstorm  covers  the  layer  of  soil  on 
the  old  snow,  and  new  soil  has  to  be  gathered  and  spread." 

Travel  and  transportation  meet  with  many  ob- 
stacles in  mountains,  apart  from  the  natural  difficul- 
ties which  come  from  steepness  of  slope  and  from 
forest  cover.  In  all  latitudes  where  snow  falls  in 
winter,  obstruction  by  snow-blockades  is  a  serious 
matter,  and  the  question  whether  it  is  better  to  tunnel, 
or  to  build  above  the  ground  and  keep  the  tracks  clear 
by  means  of  ploughs  and  snow-sheds,  is  an  important 
one  for  the  engineers  to  settle.  The  northern  trans- 
continental railroads  in  North  America,  where  they 
pass  over  the  western  mountain  ranges,  are  protected 
for  long  distances  at  critical  points  by  snow-sheds. 
These,  being  of  wood,  are  apt  to  take  fire,  and  fire 
watches  and  fire  apparatus  are  provided  for  such 
emergencies.  Below  the  latitudes  where  snow 
falls  in  considerable  quantities,  sheds  are  not  needed. 
Some  railroads  in  mountains  are  abandoned  alto- 
gether in  winter.  Floods  and  washouts,  landslides 
and  avalanches,  are  additional  handicaps.  The  fa- 
mous Uspallata  Pass,  between  Chile  and  Argentina, 
is  not  used  by  travellers  in  winter,  on  account  of  the 


LIFE  OF  MAN  IN   TEMPERATE   ZONES       309 

snow.  Traffic  then  goes  by  steamer,  by  way  of  the 
Strait  of  Magellan.  Fierce,  cold  winds,  and  the  alti- 
tude, have  been  effective  barriers  in  keeping  Tibet  so 
long  isolated,  and  will  remain  effective  barriers  in  the 
way  of  any  movement  of  troops  across  the  Tibetan 
plateau. 

Climate  and  Weather:  Some  Mental  Effects.  The 
frequent  and  sudden  weather  changes  of  the  temper- 
ate zones  affect  man  in  many  ways,  as  do  the  larger 
seasonal  changes.  The  relations  between  weather 
and  conduct  have  frequently  been  investigated. 
Professor  E.  G.  Dexter  has  made  an  extended  em- 
pirical study  of  the  effects  of  the  weather  in  relation 
to  deaths,  suicides,  the  number  of  errors  made  in 
banks,  and  misdemeanours  generally.  It  appears,  as 
one  of  the  most  interesting  general  conclusions,  that 
physically  exhilarating  weather  conditions  are  accom- 
panied by  an  abnormal  prevalence  of  excesses  in  de- 
portment, while  deaths,  suicides,  and  errors  in  banks 
show  a  decrease.  So  many  indirect  effects  come  into 
play  in  these  conditions  that  care  must  be  taken  not 
to  draw  too  hasty  conclusions.  Thus  H.  H.  Clay- 
ton has  pointed  out  that  errors  in  banks  may  be  more 
likely  on  cloudy  days  because  of  the  greater  difficulty 
in  seeing  figures,  and  also  that  fine  weather  tempts 
people  out  of  doors  and  thus  brings  them  into  con- 
tact with  o/thers,  giving  opportunities  for  crime. 
Light  wind  movement  seems  to  be  accompanied  by 
fewer  misdemeanours  in  schools ;  low  relative  humidity 
by  a  larger  percentage  of  misdemeanours ;  great  cold 


310  CLIMATE 

by  more  suicides,  and  so  on.  Bertillon  has  collected 
data  on  suicides  and  seasons  in  France,  and  Leffing- 
well  has  investigated  illegitimacy  and  the  influence  of 
seasons  on  conduct  in  Great  Britain. 

The  difference  in  the  effects  of  a  bright,  crisp  day, 
when  work  is  well  and  quickly  done,  and  of  a  dull, 
depressing,  and  enervating  day  is  well  known.  A  dis- 
mal day  is  a  dies  mail.  Strong  cyclonic  winds,  blow- 
ing polewards  from  lower  latitudes,  are  characteristic 
of  the  temperate  zones,  and  are  proverbially  disagree- 
able and  irritating,  in  strong  contrast  with  the  cooler 
winds  from  higher  latitudes.  The  sirocco  in  Italy; 
the  solano  in  Spain;  the  norte  in  Argentina,  for  ex- 
ample, are  such  winds.  The  sirocco  has  been  described 
as  "  not  fatal  to  human  life,"  but  "  deadly  to  human 
temper."  In  Spain  there  is  a  proverb,  "  Ask  no 
favour  during  the  solano."  The  nervous  effects  of 
the  dry  foehn  and  chinook  are  well  known.  The 
zonda  of  the  Argentine  is  reported  as  not  infrequently 
making  people  temporarily  insane,  and  leading  to 
suicide.  Many  other  mental  effects  of  the  weather 
might  be  noted. 

Climate,  Weather,  and  Military  Operations.  His- 
torical consequences  of  great  importance  have  fol- 
lowed from  special  conditions  of  climate  or  weather. 
Maguire's  Outlines  of  Military  Geography  (Cam- 
bridge, 1899)  contains  a  chapter  on  the  influence 
of  climate  on  military  operations,  but  this  subject  has 
hitherto  received  little  attention.  More  recently, 
Bentley,  in  a  presidential  address  before  the  Royal 


LIFE   OF  MAN  IN  TEMPERATE  ZONES       311 

Meteorological  Society,  London,  considered  the 
matter.  A  few  illustrations  only  can  here  be 
given. 

The  fleet  of  Xerxes  was  lost  in  a  storm  on  the 
coast  of  Greece.  In  54  B.C.,  owing  to  a  preceding 
drought  and  scanty  harvest,  Caesar  was  obliged  to 
scatter  his  army  in  separate  winter  quarters,  and  in 
this  situation  one  of  these  isolated  bodies  of  Romans 
wras  attacked  and  destroyed.  The  consequences  came 
near  being  very  disastrous  for  Cgesar.  A  storm  de- 
stroyed the  Spanish  Armada.  The  French  Revolu- 
tion was  precipitated  by  a  severe  winter.  Napoleon 
was  defeated  in  1796,  owing  to  the  ground  being  too 
heavy  for  the  movement  of  the  French  artillery.  In 
1796,  also,  Gen.  Hoche's  fleet,  sailing  for  Ireland, 
was  scattered  by  a  storm.  The  terrible  winter  retreat 
of  the  French  from  Moscow  furnished  a  vivid  illus- 
tration of  the  strength  of  the  two  invincible  Russian 
generals,  January  and  February  (to  use  a  Russian 
expression).  The  battle  of  Waterloo  was  postponed 
on  account  of  a  heavy  rainfall.  The  siege  of 
Sebastopol  furnished  another  illustration  of  the  suf- 
fering which  a  severe  winter  may  produce.  The 
"  Boxer  "  outbreak  in  China,  in  1900,  was  precipi- 
tated by  a  scarcity  of  rain  in  the  preceding  autumn, 
bringing  on  destitution  and  famine,  and  driving  the 
people  to  pillage  and  robbery.  During  the  fighting 
around  Tientsin,  early  in  July,  the  situation  of  the 
allied  troops  was  very  critical  when  a  torrential  rain- 
fall compelled  the  Chinese  to  retire.  During  the  Boer 


312  CLIMATE 

war  there  were  many  instances  of  weather  controls 
over  military  operations.  On  January  9,  1900,  a 
heavy  rain  checked  the  fighting  near  Ladysmith,  and 
cloudy  weather  often  prevented  the  use  of  the  helio- 
graph in  communicating  with  Ladysmith.  During 
the  recent  British  campaign  in  Tibet,  great  difficulty 
was  experienced  at  the  higher  altitudes,  owing  to  the 
hardening  of  the  oil  in  the  guns  on  account  of  the 
cold,  and  the  low  boiling  point  made  it  difficult  to 
cook  food  properly  in  the  absence  of  cooking  utensils 
adapted  for  use  at  low  pressures.  In  the  Russo- 
Japanese  war,  the  cold  and  heat  and  rain  made  them- 
selves felt  as  powerful  factors  in  the  campaign. 

The  effect  of  even  one  rain  may  be  far-reaching. 
It  has  been  said  that  a  shower  of  rain  acts  like  a  wet 
blanket  on  a  mob.  Numerous  recent  illustrations  of 
the  truth  of  this  statement  are  available.  A  rain  in 
Paris  on  the  day  of  the  Dreyfus  verdict,  in  Septem- 
ber, 1899,  doubtless  helped  to  prevent,  if  it  did  not 
actually  prevent,  an  outbreak.  During  a  great  strike 
in  Moscow  at  the  end  of  January,  1905,  a  snowstorm 
greatly  helped  the  authorities  in  keeping  the  people 
off  the  streets.  Again,  on  April  6,  1906,  at  St. 
Petersburg,  a  steady  downpour  of  rain  all  day  pre- 
vented an  open-air  meeting  which  would  doubtless 
have  led  to  conflict  with  the  military. 

Railroads.  Railroads  have  reached  their  greatest 
development  in  the  continental  climates  of  the  tem- 
perate zones,  and  the  influence  of  these  climates  upon 
the  construction  and  operation  of  these  roads  is  far- 


LIFE  OF  MAN  IN  TEMPERATE  ZONES       313 

reaching,  varied,  and  of  the  greatest  economic  im- 
portance. Transportation  by  rail  is  necessarily 
closely  affected  by  weather  conditions,  for  trains  have 
no  protection  against  snow,  or  wind,  or  heat.  The 
extremes  of  heat  and  cold  have  a  racking  effect 
upon  all  iron  and  steel  work,  and  careful  allowance 
has  to  be  made  for  this  factor.  Floods  wash  away 
bridges,  tracks,  and  ballast.  In  the  Mississippi  basin 
of  the  United  States,  floods  in  1903  cost  the  Sante  Fe 
Railroad  alone  $1,000,000.  Stormy  weather  means 
bad  country  roads,  and  this  may  prevent  the  trans- 
portation of  farm  products  to  the  railroads,  and  thus 
result  in  irregularity  in  the  supply  of  freight.  It  is 
believed  that  were  freight  delivered  regularly,  the 
railroads  would  find  it  possible  to  use  less  rolling 
stock,  with  better  returns. 

Many  of  the  most  obvious  climatic  handicaps  are 
seen  in  the  more  northern  latitudes  of  the  north  tem- 
perate zone,  where  the  winter  brings  snow  and  ice. 
The  trans-Siberian  Railway  was  constructed  with 
great  difficulty  because  of  frozen  soil,  spring  thaws, 
and  upheaved  tracks.  Across  the  rivers  and  across 
Lake  Baikal,  rails  were  laid  on  the  ice  during  con- 
struction times.  Later,  the  trains  were  carried  across 
the  lake  in  winter  on  ice-breaking  ferryboats.  The 
houses  for  the  labourers  were  also  built  on  the  ice. 
Work  was  /greatly  interrupted  during  the  winter. 
On  the  Great  Lakes  of  North  America,  temporary 
rails  are  laid  on  the  ice  during  the  ice-cutting  season. 
The  new  trans-Canadian  railway  lines  will  traverse 


314  CLIMATE 

a  region  of  severe  cold  in  winter,  but  generally  of 
moderate  snowfall,  and  although  situated  far  to  the 
north,  they  will  draw  upon  a  splendid  wheat  crop, 
favoured  by  the  warmth  and  well-distributed  rains 
of  summer.  The  snow-blockades  on  the  northern 
railroads  of  America  led  to  the  invention  and  use  of 
the  ingenious  and  effective  rotary  snow-plough ;  to  the 
planting  of  trees  along  the  right  of  way  to  serve  as 
snow-breaks,  and  to  the  construction  of  snow-fences. 
In  Siberia,  the  snow  itself  is  occasionally  piled  up  in 
heaps  by  means  of  ploughs  or  shovels,  and  is  thus 
made  to  serve  as  a  windbreak.  The  campaign  of  a 
modern  electric  street  railway  system,  in  an  American 
city,  against  the  winter's  snow,  is  carefully  planned  in 
the  preceding  summer,  and  every  detail  is  worked  out 
beforehand.  A  mild,  open  winter  in  latitudes  where 
winter  snowfall  is  an  important  factor  in  railroad 
operation,  means  a  saving  of  money,  time,  and  labour, 
which  results  in  increased  earnings  and  even  in  larger 
dividends.  The  motive  power  which  is  otherwise 
employed  in  fighting  snow  is  then  earning  money  for 
the  company. 

In  the  warmer  latitudes  and  drier  seasons  the  blow- 
ing sand  and  dust  are  disagreeable,  and  even  delay 
transportation  at  times.  High  temperatures  and 
heavy  rainfall  hasten  the  decay  of  railroad  ties.  The 
growth  of  weeds  on  the  right  of  way  of  earth-ballasted 
roads  is  a  considerable  difficulty  in  many  parts  of  the 
temperate  zones,  as  well  as  in  the  tropics.  In  the 
United  States,  the  Union  Pacific  Railroad  has  used 


LIFE  OF  MAN  IN  TEMPERATE  ZONES      315 

a  gasoline  weed-burner,  which  scorches  off  the  vegeta- 
tion, and  the  salt  water  of  Great  Salt  Lake,  sprinkled 
over  the  road-bed,  has  also  been  found  to  serve  well 
as  a  weed-destroyer. 

The  state  of  the  weather  sometimes  fixes  the  load 
of  an  engine,  as  in  the  case  of  freight  trains  running 
west  from  Pittsburg,  Pennsylvania.  According  to 
the  weather  forecast  of  favourable,  reasonably  good, 
bad,  and  very  bad  weather,  the  load  of  a  freight  en- 
gine varies  from  1750  tons  to  1225  tons.  The  busi- 
ness of  railroads  depends  largely  upon  the  season, 
but  the  time  at  which  these  roads  are  generally  the 
most  useful,  and  also  the  most  overburdened,  is  after 
harvest-time.  Then,  in  the  great  wheat  regions  of 
North  America,  the  immense  crops  can  with  difficulty 
be  handled  and  stored,  and  the  need  of  money  to 
"  move  the  crops  "  not  infrequently  leads  to  financial 
readjustment  and  stringency  in  the  money  market. 

Transportation  by  Water.  The  oceans  at  the 
equatorward  margins  of  the  temperate  zones  have 
the  light,  variable  winds  and  calms  of  the  horse  lati- 
tude belts,  with  the  seasonal  change  from  trades  to 
westerlies,  and  back  again.  From  the  Mediterranean, 
a  fairly  calm  sea  with  few  storms,  came  many  of  the 
early  navigators  and  explorers,  doubtless  tempted  to 
sea  by  the  regularity  and  steadiness  of  their  winds 
and  by  the  clearness  of  the  air  which,  before  the  days 
of  lighthouse,  compass,  and  telescope,  aided  naviga- 
tion by  making  it  easy  to  see  distant  landmarks.  In 
the  higher  latitudes,  the  prevailing  westerlies,  blowing 


316  CLIMATE 

\vith  moderate  to  high  velocity  and  frequently 
disturbed  by  storms,  especially  in  winter,  generally 
favour  voyages  to  the  eastward,  but  are  head  winds 
for  vessels  sailing  westward.  The  voyage  from 
Europe  to  North  America  is  not  an  easy  one  for  sail- 
ing ships,  for,  in  addition  to  the  head  winds,  there  is 
also  the  danger  of  ice  and  of  fog  on  the  Banks  of 
Newfoundland.  The  sailing  route  from  Europe  to 
North  America  by  way  of  the  north-east  trade,  and 
back,  more  directly,  in  the  westerlies,  makes  effective 
use  of  these  two  great  wind  systems.  To  keep  clear 
of  ice  and  fog,  the  North  Atlantic  steamer  routes  at 
certain  seasons  keep  farther  to  the  south,  with  the 
disadvantage  of  lengthening  the  distance  travelled. 
Ocean  currents,  which  are  meteorological  phenomena 
because  wind-driven,  are  important  factors  in  con- 
trolling the  location  of  sailing  routes.  The  voyage 
around  Cape  Horn  to  the  westward,  in  the  teeth  of 
boisterous  westerly  gales,  is  much  dreaded  by  sea- 
men. Outward-bound  vessels  from  England  to 
Australia  find  it  convenient  to  sail  by  the  Cape  of 
Good  Hope,  while  on  the  homeward  voyage  they  can 
round  Cape  Horn  to  the  eastward.  By  so  doing 
they  have  a  good  chance  of  fair  winds  all  the  way. 
The  most  favourable  weather  condition  for  pass- 
ing Cape  Horn  to  the  westward  is  the  presence,  dur- 
ing the  period  necessary  for  rounding  the  Horn  and 
for  crossing  latitude  50°  S.  in  the  Pacific,  of  a  centre 
of  low  pressure  in  the  immediate  vicinity  of  the  Cape, 
and  not  too  far  to  the  southward.  This  pressure  dis- 


LIFE   OF  MAN  IN   TEMPERATE  ZONES       317 

tribution  gives  north-east,  east,  and  south-east  winds 
in  succession  in  the  case  of  a  west-bound  vessel  which 
passes  the  centre  to  the  southward.  The  cyclones  of 
the  westerlies  are  always  more  or  less  of  a  hindrance 
and  danger  to  shipping.  Storm  winds  have,  it  is 
true,  accidentally  led  to  the  discovery  of  new  lands, 
but  stormy  seas  do  not  tempt  man  to  sail  upon  them. 
Protected  harbours  are  naturally  sought ;  unprotected 
harbours  are  provided  with  breakwaters  and  docks; 
low-lying  coasts,  like  those  of  Germany  and  Holland, 
are  subject  to  damage  and  flooding,  and  even  loss  of 
life,  by  storm  waves  and  high  tides.  Even  on  the 
borders  of  the  temperate  zones,  in  the  sub-tropical 
belts,  the  winter  cyclones  of  the  westerlies  occasion- 
ally give  rise  to  gales  dangerous  to  shipping,  as  on 
the  coast  of  California  and  of  Chile.  When  a  strong 
norte  blows  at  Valparaiso,  as  it  sometimes  does  in 
the  winter  season,  the  vessels  at  anchor  in  the  har- 
bour are  obliged  to  steam  or  to  be  towed  out  into  the 
open  ocean,  in  order  to  avoid  being  blown  ashore. 
The  vessels  in  this  harbour  are  anchored  at  both  bow 
and  stern,  always  facing  the  north. 

The  freezing  of  harbours  at  the  termini  of  the  north- 
ern railroads  is  a  serious  handicap  in  many  countries. 
Ice-breakers  are  used  by  Russia  at  Vladivostock;  and 
at  Hango,  Cronstadt,  St.  Petersburg,  and  other  ports 
on  the  Baltic,  Germany's  northern  ports  suffer  more 
or  less  from  the  inconvenience  of  ice  in  winter.  The 
closing  and  opening  to  navigation  of  the  grain  ports 
is  a  matter  of  the  greatest  importance  in  the  world's 


318  CLIMATE 

grain  trade.  Canada  is  much  handicapped  by  the 
freezing  of  the  St.  Lawrence  River.  The  trans-At- 
lantic steamers  change  their  sailings  in  winter  to  ports 
that  are  accessible  the  year  around.  It  has  been  pro- 
posed to  use  an  ice-breaker  to  keep  the  St.  Lawrence 
open  longer  in  the  fall,  and  to  break  up  the  ice  earlier 
in  the  spring.  The  projected  route  from  Canada  to 
Europe  by  way  of  Hudson's  Bay  is  obviously  greatly 
handicapped,  if  not  rendered  wholly  impracticable, 
by  the  winter  ice.  On  the  frozen  Gulf  of  Finland  a 
considerable  population  of  fishermen  live  on  the  ice 
for  several  months;  building  houses  for  themselves 
and  abandoning  for  a  time  their  usual  occupation  of 
farming.  On  the  frozen  Neva,  at  St.  Petersburg, 
street  traffic  goes  on  as  on  dry  land;  roads  are  made 
over  the  ice;  the  streets  are  lighted;  cars  are  run  and 
fairs  are  held. 

Various  Effects  of  the  Weather.  Effects  of  vary- 
ing conditions  of  seasons  and  weather  are  observable 
on  all  sides.  The  march  of  the  seasons  brings  a  suc- 
cession of  occupations.  Thus  farming,  building, 
painting,  and  outdoor  work  generally,  are  prominent 
occupations  in  the  warmer  months  in  much  of  the 
temperate  zones.  Lumbering,  ice-cutting,  and  snow- 
shovelling  are  distinctly  occupations  of  the  colder 
months  in  the  higher  temperate  latitudes  in  the  United 
States.  In  North  America  the  harvesting  of  the 
cereal  crops  calls  for  thousands  of  harvest  hands 
every  summer,  many  of  whom  begin  work  in  the  south 
and  gradually  work  north  into  Canada,  as  the  crop 


LIFE   OF  MAN  IN  TEMPERATE   ZONES       31! 

comes  later  and  later  in  the  season  with  increasing 
latitude.  It  is  worth  noting,  in  passing,  that  the 
wheat  harvest  in  Argentina  usually  begins  late  in 
November  in  the  north,  and  progresses  southward 
until  February;  in  India,  the  harvest  begins  late 
in  February  in  the  south  and  progresses  northward 
until  early  in  May.  The  Indian  and  Argentine 
wheat  thus  come  to  market  in  what  is  known  as  the 
"  dead  season "  in  the  other  wheat  countries,  and 
therefore  have  an  important  effect  on  prices. 

Rainfall,  insufficient  in  quantity  or  poorly  dis- 
tributed, leads  to  a  failure  of  the  crops,  and  one  or 
more  years  of  crop  failure  may  bring  on  a  general 
financial  depression.  Even  political  overturns,  as 
has  been  shown  by  Clayton  for  the  United  States, 
have  been  brought  about  by  deficient  rainfall  result- 
ing in  short  crops,  and  a  similar  occurrence  has  not 
been  unknown  in  England.  Political  consequences 
following  crop  failure  have  been  traced  to  the  oc- 
currence of  destructive  hot  winds  in  Kansas  in  1890 
and  1891,  which  gave  the  Populist  Party  national 
importance.  The  financial  value  of  one  rain,  at  a 
critical  time  of  drought,  can  sometimes  be  approxi- 
mately estimated.  In  Kansas  and  Nebraska,  in  1900, 
the  value  of  one  rain,  lasting  twenty-four  hours, 
in  saving  the  corn  crop  was  put  at  over  $80,000,000. 
In  Australia*,  the  wheat  crop,  as  has  been  shown  by 
Wills,  is  so  closely  related  to  rainfall  that  the  ratio 
of  wheat  in  bushels  per  acre  and  the  annual  rainfall 
in  inches  has  been  made  out  to  be  a  remarkably 


CLIMATE 

definite  one.  Similarly,  the  number  of  sheep  per 
square  mile  in  Australia  and  in  Argentina  depends 
very  closely  upon  the  rainfall,  as  has  also  been  shown 
by  Wills.  Unseasonable  weather,  at  any  time  of  year, 
disturbs  trade,  which  is  very  closely  adjusted  to  the 
normal  weather  conditions  that  may  reasonably  be 
expected  at  any  given  time.  Strikes  have  come  to 
an  end  because  of  the  approach  of  cold  weather,  and 
the  prospects  of  suffering  among  the  strikers;  and 
strikes  have  continued  during  great  heat  because  of 
the  desire  of  the  men  to  remain  idle  at  such  times. 
Certain  atmospheric  conditions  seem  to  be  more 
favourable  than  others  to  spontaneous  combustion. 
A  dense  London  fog  causes  a  heavy  money  loss  in 
the  extra  expense  for  gas  and  electric  light,  arid  in 
the  delay  and  damage  to  shipping.  It  has  been  esti- 
mated that  the  cost  of  the  gas  burned  during  one  day 
of  an  ordinary  London  fog  approximates  $15,000. 
In  New  York  city,  the  coming  of  a  summer  afternoon 
thunder  storm  is  reported  by  watchmen  to  the  electric- 
light  power-houses,  where  the  dynamos  are  set  going 
at  full  speed  in  order  to  supply  the  sudden  demand 
for  extra  light.  In  England,  a  good  deal  of  business 
is  done  by  insurance  companies  in  indemnifying 
cricket  clubs  against  loss  in  case  an  important  game 
happens  to  be  interfered  with  by  rain.  So  many 
claims  have  arisen  for  the  insurance  money  that  it 
lias  become  customary  in  such  cases  to  stipulate  what 
amount  of  rain  shall  fall  in  order  that  the  claim  shall 
be  paid.  Insurance  against  damage  by  tornadoes, 


LIFE  OF  MAN  IN  TEMPERATE  ZONES       321 

lightning,  hail,  etc.,  illustrates  the  efforts  of  man  to 
guard  against  loss  due  to  hostile  features  of  his 
weather  and  climate.  The  danger  from  tornadoes 
on  the  western  plains  and  prairies  of  the  United 
States  has  led  to  the  building  of  underground  "  dug- 
outs," or  tornado  cellars,  which  are  somewhat  akin  to 
the  underground  winter  dwellings  of  some  of  the 
natives  tribes  of  northern  Siberia,  built  as  a  protection 
against  winter  storms.  Such  illustrations  might  be 
multiplied  indefinitely. 


CHAPTER  X 

THE  LIFE  OF  MAN  IN  THE  POLAR  ZONES 

General:  A  Minimum  of  Life — Culture — Subdivisions  of  the 
Arctic  Zone — Characteristics  of  the  Tundra — The  Reindeer — 
Population  and  Occupations — Dwellings — Food  and  Clothing 
—Iceland— The  Polar  Ice  Cap:  The  Eskimo — Dwellings- 
Food  and  Clothing — Travel  and  Transportation — Occupations 
and  Arts — Customs — Deserts  of  Sand  and  Deserts  of  Snow. 

General:  A  Minimum  of  Life.  The  conditions  of 
life  are  necessarily  very  specialised  under  the  peculiar 
climatic  features  which  are  met  with  in  the  polar 
zones.  A  "  monotony  of  cold  "  replaces  the  "  mono- 
tony of  heat "  of  the  tropics,  and  instead  of  the  spur 
of  the  temperate  zone  seasons  there  is  the  depressing, 
long,  polar  night.  There  is  a  minimum  of  life,  but 
life  is  more  abundant  in  the  north  polar  than  the 
south  polar  zone,  and  our  knowledge  is  confined 
chiefly  to  the  former  area.  Plants  are  few  and 
lowly.  In  the  farther  north,  only  a  few  mosses  and 
lichens  are  found.  Land  animals  which  depend  upon 
plant  food  must  therefore  likewise  be  few  in  number. 
Farming  and  cattle-raising  cease.  The  reindeer, 
which  manages  to  find  sufficient  food  in  the  lowly 
.rctic  vegetation,  is  the  mainstay  of  many  of  the 

322 


LIFE  OF  MAN  IN  POLAR  ZONES  323 

Arctic  natives.  But  the  reindeer  must  wander  far 
and  wide  in  search  of  their  moss.  And  many  rein- 
deer are  needed  to  provide  sustenance  for  one  man. 
Population  is  small  and  scattered.  There  are  no 
permanent  settlements  at  all  within  the  Antarctic 
circle.  And  the  few  scattering  islands  in  the  im- 
mediately surrounding,  vast  ocean  area  of  the  south 
temperate  zone  are  likewise  uninhabited,  except  tem- 
porarily by  shipwrecked  seamen  or,  lately,  by  mem- 
bers of  scientific  parties.  In  the  Arctic  area  human 
settlements  are  fairly  well  scattered  over  a  consider- 
able range  near  the  margins  of  the  zone,  but  with 
increasing  latitude  man  is  more  and  more  rarely  seen, 
and  finally  he  disappears  entirely.  There  will  never 
be  permanent  human  settlements  at  the  poles.  Life 
is  hard;  a  constant  struggle  for  existence.  Man  seeks 
his  food  by  the  chase  on  land,  but  chiefly  in  the  sea. 
Hardly  a  tenth  of  Greenland's  population  could  live 
there  without  food  from  the  sea.  It  has  been  well 
said  that  with  every  degree  of  higher  latitude  man  is 
more  forced  to  obtain  his  food  supply  from  the  sea. 
He  lives  along,  or  near,  the  sea  coast.  The  interior 
lands,  away  from  the  sea,  are  deserted.  Gales,  and 
snow,  and  cold,  cause  many  deaths  on  land,  and  also 
at  sea,  especially  during  fishing  expeditions.  It  has 
been  estimated  that  about  one  twenty-fifth  of  the 
population  of  Iceland  perishes  through  being  lost  in 
snowstorms,  by  freezing,  or  by  drowning.  In  the 
Faroe  Islands  about  8%,  and  in  Greenland  7%  of 
the  deaths  have  been  reported  as  due  to  drowning 


324  CLIMATE 

accidents  of  one  sort  or  another.  Rink  has  reported 
of  Greenland  that  most  of  the  deaths  occur  at  sea- 
sons of  most  profitable  sealing  operations.  Such  dif- 
ficult conditions  of  securing  food  make  famine  a  likely 
occurrence.  If  a  successful  hunting  or  sealing  ex- 
pedition follows  a  time  of  famine,  the  natives  are 
wont  to  indulge  in  the  most  revolting  gorges.  The 
polar  limit  of  permanent  human  settlements  is  be- 
lieved by  Eessels  to  be  fixed,  not  by  the  decreasing 
temperature,  but  by  the  increase  in  the  length  of  the 
night,  which  shortens  the  time  during  which  man  can 
lay  up  food  by  hunting  and  fishing,  to  last  him 
through  the  polar  night.  The  chase  after  land  ani- 
mals has  helped  to  drive  the  latter  farther  and 
farther  north. 

Culture.  Under  such  adverse  conditions  it  is  not 
hard  to  see  that  progress  towards  a  higher  culture  is 
not  a  reasonable  expectation.  There  is  no  time  in 
which  man  may  seek  to  develop  and  satisfy  his  higher 
needs.  Much  truth  is  contained  in  Guyot's  some- 
what picturesque  statement:  "  The  man  of  the  polar 
regions  is  the  beggar  overwhelmed  with  suffering, 
who,  too  happy  if  he  but  gain  his  daily  bread,  has  no 
leisure  to  think  of  anything  more  exalted."  Thus 
the  inhabitants  of  the  north  polar  zone  have  not  played 
an  important  role  in  the  history  of  human  progress. 
A  sparse  population,  not  far  advanced  in  culture  or 
in  social  relations,  is  inevitable  under  polar  conditions 
of  climate.  Yet  the  courage  of  the  Eskimo  in  brav- 
ing a  raging  sea  in  his  kayak,  or  in  facing  a  polar 


LIFE  OF  MAN  IN  POLAR  ZONES 

bear;  the  docility,  industry,  good  nature,  and  other 
attractive  qualities  of  these  people,  which  have  been 
described  by  more  than  one  Arctic  explorer;  the  in- 
telligence and  the  patience  with  which  they  have 
overcome  the  disadvantages  of  their  environment; 
the  contributions  made  by  Iceland  to  the  world's 
literature — these  and  other  similar  considerations 
make  us  pause  before  passing  too  hasty  a  judgment. 
Polar  cold  has  not  produced  a  distinct  type  of  polar 
man,  but  the  general  effect  of  the  polar  climate  in 
eliminating  cattle-raising  and  agriculture — except  to 
a  very  limited  extent,  and  in  a  few  favoured  localities 
— from  the  list  of  human  occupations ;  in  turning  man 
to  the  sea  for  his  food ;  in  magnifying  the  importance 
of  animal  products,  especially  bones,  in  the  produc- 
tion of  domestic  utensils  and  weapons,  is  more  or  less 
familiar  among  all  Arctic  tribes.  There  is  no  steady, 
profitable  occupation  in  which  large  numbers  of  men 
may  be  regularly  employed  at  good  wages.  Broad, 
general  analogies  have  been  traced  between  the 
northern  Eskimos  and  the  Fuegians  of  far  southern 
South  America. 

Subdivisions  of  the  Arctic  Zone.  For  the  purpose 
of  this  consideration  the  north  polar  zone  may  con- 
veniently be  subdivided  into  (1)  the  lowlands  of  the 
tundra,  where  the  summer  sun  melts  off  the  snow  and 
thaws  out  the  upper  few  inches,  or  possibly  few  feet, 
of  the  frozen  ground,  and  (2)  the  permanently  ice- 
and  snow-covered  higher  land,  where  the  heat  of  the 
summer  does  not  remove  the  icy  cover,  and  where 


326  CLIMATE 

man,  so  far  as  he  inhabits  those  districts  at  all,  must 
live  along  the  margins  of  the  ice-cap,  near  the  sea.  In 
whichever  portion  of  the  Arctic  man  is  found,  his 
general  mode  of  life,  his  occupations,  his  dwellings, 
food,  clothing,  arts,  and  so  on,  are  rigidly  controlled 
by  climate. 

Characteristics  of  the  Tundra.  The  low-lying 
frozen  desert  along  the  shores  of  the  Arctic  Ocean 
is  known  as  the  tundra.  "  Barren  Lands  "  is  the 
name  by  which  it  goes  in  Canada.  Through  belts  of 
lowly,  scattering  trees,  these  lowlands  gradually 
merge  on  the  south  into  the  northernmost  forests  of 
the  temperate  zone.  To  the  north  are  eternal  snow 
and  ice.  Over  the  treeless  tundra  the  soil  is  per- 
manently frozen  to  a  great  depth,  but  the  upper  part 
of  the  surface  thaws  out  sufficiently  during  the  sum- 
mer to  produce  a  great  plain,  more  or  less  swampy, 
which  may  become  dry  in  places  in  midsummer. 
Scattered  clumps  of  trees,  chiefly  along  the  water- 
courses, relieve  the  monotony  of  the  dead-level  here 
and  there,  and  during  the  summer  the  tundra  is  cov- 
ered for  a  few  weeks  with  lowly  lichens,  mosses,  and 
ferns,  or  even  with  the  green  leaves  of  stunted  berry- 
bushes,  whose  roots  are  all  near  the  surface.  At  this 
season,  also,  brilliant  flowers,  insects,  and  birds  give 
life  and  charm  to  the  scene.  With  their  polar  char- 
acteristic of  an  extraordinarily  rapid  growth,  under 
the  summer  sun,  the  plants  of  the  tundra  awaken  as 
if  by  magic.  The  summer  is  in  striking  contrast 
with  the  winter,  wrhen  these  great  plains  are  frozen 


LIFE  OF  MAN  IN  POLAR  ZONES  327 

solid,  rivers  and  all,  under  a  broad  sheet  of  snow. 
Journeys  by  dog  or  reindeer  sledge,  or  on  skis,  can 
be  made  in  any  direction,  regardless  of  the  presence 
of  water  or  land  beneath  the  snows,  the  routes  to  be 
followed  being  accurately  indicated  by  means  of 
landmarks.  Thus  in  the  Yukon  country  of  Alaska, 
as  long  as  the  rivers  remain  frozen,  dog-sledges  are 
used  in  the  interior  to  carry  the  mails  and  other 
freight.  This  is  much  more  expensive  than  the  sum- 
mer transportation  by  boat.  When  the  snow  is  in 
good  condition,  the  natives  can  travel  at  the  rate  of 
fourteen  or  fifteen  miles  an  hour  on  skis.  In  spring 
and  early  summer,  when  the  upper  portions  of  north- 
ward flowing  rivers  melt,  while  the  lower  portions  are 
still  frozen,  floods  are  frequent  over  the  lowlands.  In 
the  transition  season,  when  the  rivers  are  not  frozen 
and  the  ground  is  not  snow-covered,  travel  is  usually 
difficult  or  impossible.  In  the  month  of  October,  in 
northern  Russia,  for  example,  the  government  mail 
service  is  discontinued,  labour  contracts  are  off,  and 
the  keepers  of  stages  are  freed  from  their  usual  obli- 
gations. The  fact  that  her  northern  ports  are  ice- 
bound in  winter  is  a  serious  handicap  to  Russia.  This 
was  one  of  the  principal  reasons  for  her  desire  to  se- 
cure an  ice-free  port  on  the  Pacific,  Vladivostock,  the 
original  terminus  of  the  trans-Siberian  Railroad, 
being  also  ice-bound  in  winter.  This  led  to  the  ac- 
quisition of  Port  Arthur,  and  eventually  to  the  war 
with  Japan.  An  open  port  would  be  an  immense 
gain  for  Russia,  which  has  been  much  handicapped 


328  CLIMATE 

in  training  her  sailors  by  the  freezing  of  the  Baltic 
harbours  in  winter. 

The  Reindeer.  The  reindeer  in  Eurasia  and  the 
caribou  in  North  America  are  the  most  important  ani- 
mals of  the  tundra.  They  feed  on  lichens  and  mosses, 
or  stunted  shrubs.  The  reindeer  is  wonderfully 
adapted  to  the  natural  conditions  under  which  it 
lives.  With  wide  hoofs,  well-fitted  for  travel  over 
the  snow,  it  moves  very  swiftly.  Able  to  endure 
great  cold,  it  scrapes  through  the  snow  in  winter  to 
find  the  reindeer  moss  on  which  it  feeds.  It  migrates 
northward  in  summer  and  southward  to  the  forests 
in  winter,  in  search  of  food.  The  reindeer  has  been 
partly  trained  as  a  domestic  animal  by  the  natives  of 
the  tundra.  To  them,  the  reindeer  is  of  the  utmost 
importance:  a  man's  wealth  is  rated  according  to  the 
number  of  these  animals  in  his  possession,  and  their 
loss,  by  reason  of  famine  or  disease,  usually  means 
that  the  owners  are  reduced  to  poverty.  The  rein- 
deer supplies  milk  and  flesh  for  food;  it  is  an  excel- 
lent draught  animal;  its  skin,  and  sinews,  and  bones 
furnish  material  for  clothing,  tents,  and  utensils  and 
weapons  of  all  sorts. 

Population  and  Occupation.  The  scattered  nom- 
adic tribes  of  the  tundra,  a  semi-pastoral  and  semi- 
hunting  population,  wander  about  with  their  reindeer 
over  the  vast  stretches  of  the  tundra,  stopping  wher- 
ever the  animals  find  food;  having  no  settled  abode; 
making  little  progress  in  the  cultivation  of  the  higher 
arts.  Population  is  inevitably  sparse,  and  will  so  re- 


LIFE  OF  MAN  IN  POLAR  ZONES  329 

main.  The  Lapps;  the  Eskimos,  along  the  borders 
of  the  Arctic  Ocean;  the  Samoyads,  Yakuts,  Ostyaks, 
Tunguses — all  have  a  common  mode  of  life.  Hunt- 
ers and  fishermen  by  force  of  circumstances,  they 
can  never  become  farmers.  In  winter,  they  hunt  for 
small  fur-bearing  animals  or  for  larger  game  along 
the  borders  of  the  southern  forests.  In  summer,  they 
fish  in  the .  rivers  or  along  the  shores,  storing  away 
food  for  the  winter.  They  are  always  on  the  move. 
Some  of  the  tribes  live  along  the  forest  borders  in 
the  winter,  for  the  sake  of  the  shelter  there  provided. 
The  men  procure  food  and  make  the  needed  imple- 
ments and  weapons.  The  women  prepare  the  food 
and  clothing;  watch  the  reindeer;  collect  berries  in 
summer;  dry  the  fish;  and  even  take  charge,  among 
the  Samoyads  and  Ostyaks,  for  example,  of  setting 
up  and  taking  down  the  tents,  in  order  that  the  men 
may  have  more  time  for  the  chase.  The  ill,  the  weak, 
and  the  aged  receive  little  attention. 

Dwellings.  The  inhabitants  of  the  tundra  protect 
themselves  against  the  inclemencies  of  the  weather  in 
summer  by  means  of  portable  tents  made  of  skins  or 
bark,  supported  by  poles.  In  winter,  the  structure 
is  often  more  substantial,  having  more  coverings  or 
being  made  of  turf,  or,  in  the  case  of  some  of  the 
Lapps,  even  of  snow.  Where  timber  is  scarce,  far 
from  forests,  the  Samoyads  and  Ostyaks  consider 
their  tent-poles  very  valuable  property,  and  carry 
them  along  with  the  greatest  care.  The  tribes  who 
live  nearer  the  forests  do  not  take  the  trouble  to 


330  CLIMATE 

transport  the  tent-poles  when  they  move.  In  the 
far  north,  away  from  the  forests,  driftwood  is  an  im- 
portant source  of  lumber  supply.  The  furnishings 
are  very  simple  and  easily  moved  when  tents  are 
struck.  Furs  and  skins  are  the  principal  articles  of 
trade  among  the  inhabitants  of  the  tundra. 

Food  and  Clothing.  The  natural  food  is  obtained 
chiefly  from  the  reindeer  and  other  land  animals  and 
wrild  fowl,  whose  flesh  is  often  eaten  raw.  Reindeer 
milk,  fish,  berries,  and  a  little  other  vegetable  food, 
are  occasionally  added  to  the  monotonous  and  unat- 
tractive diet  list,  as  is  fresh  or  dried  blood.  Trade 
with  the  neighbouring,  more  highly  civilised  people 
on  the  south  gives  tea  and  coffee,  tobacco,  and  other 
articles  of  food.  In  northern  Alaska  caribou,  bear, 
salmon,  rabbits,  grouse,  and  ptarmigan  make  up  the 
principal  food  of  the  natives. 

The  clothing  of  the  tundra  tribes  shows  climatic 
control  in  the  character  and  in  the  simplicity  of  the 
materials  used.  Furs  and  skins  are  universally  em- 
ployed. The  Samoyads,  Tunguses,  and  others  often 
ornament  their  furs  with  bands  of  brightly  coloured 
stuffs,  when  these  can  be  secured.  Mittens,  caps, 
and  boots  of  fur  are  essential  for  protection  against 
the  winter  cold.  Implements  of  the  chase  and  do- 
mestic utensils  are  ingeniously  made  of  wood,  when 
available,  or  of  the  skin,  sinews,  and  bones  of  the 
reindeer.  Needles  and  spoons  are  commonly  made 
of  bone ;  for  thread,  gut  is  used.  It  is  worth  noting 
that  the  fossil  elephants  found  frozen  in  the  gravelly 


LIFE  OF  MAN  IN  POLAR  ZONES  331 

river  banks  of  the  Siberian  tundras  have,  ages  later, 
furnished  ivory  for  the  Chinese  to  fashion  into  their 
delicate  and  beautiful  carvings. 

Iceland.  Although  outside  of  the  Arctic  circle, 
Iceland  is  within  the  polar  zone  according  to  Supan's 
classification.  Its  climatic  conditions  are,  however, 
peculiar  on  account  of  its  being  an  island,  exposed  to 
the  tempering  influence  of  the  warm  Atlantic  waters. 
Favoured  as  it  is,  the  climate  is  unsuitable  for  grain, 
breadstuffs  and  other  articles  of  food  being  imported. 
Sheep,  cattle,  and  horses  are  raised,  and  fish,  feathers, 
skins,  horses,  wool,  tallow,  and  other  local  products 
are  exported.  The  summer  is  the  natural  time  for 
travel,  by  land  or  water,  and  for  this  reason,  the 
judicial  assemblies  have  in  the  past  been  held  in  that 
season.  The  natives  of  Iceland,  although  much 
handicapped,  have  played  their  part  in  the  world's 
progress,  as  enterprising  sailors  and  discoverers,  and 
have  developed  a  literature. 

The  Polar  Ice-Cap:  The  Eskimo.  The  polar  peo- 
ple par  excellence,  the  Eskimos,  live  characteristically 
on  the  margins  of  the  Arctic  ice-cap,  beyond  the 
tundra,  along  the  shores  of  the  Arctic  seas.  The 
Eskimo,  in  common  with  other  Arctic  natives,  must 
secure  his  food  almost  wholly  from  the  sea.  When 
he  needs  to  travel  to  any  distance  for  food,  he  moves 
his  dwelling;  He  is  necessarily  nomadic  in  his 
habits.  His  existence  is  in  many  ways  not  unlike 
that  of  the  hunting  tribes  of  the  equatorial  forests. 

Dwellings.     The     rude     but     substantial     dome- 


332  CLIMATE 

shaped  ice  or  snow  hut  (igloo)  of  the  Eskimo  furn- 
ishes one  of  the  most  striking  illustrations  of  the 
climatic  control  over  human  dwellings.  Built  low, 
and  entered  by  a  low  passageway,  the  doorway  may 
be  closed  with  a  block  of  ice  or  snow,  and  thus  cold 
and  drifting  snow  and  prowling  animals  are  kept 
out.  The  igloos  are  furnished  with  the  simplest 
utensils — a  "  stove  "  or  lamp  to  give  heat  and  light, 
with  blubber  for  fuel  and  oil,  and  dried  moss  for  a 
wick ;  a  dish  for  melting  ice  for  drinking  purposes,  and 
for  heating  the  seal  or  other  meat.  A  clear  sheet  of 
ice,  made  air-tight  by  having  water  poured  over  it,  not 
infrequently  does  duty  as  a  window  as  effectively  as 
a  pane  of  glass,  and  is  even  preferred  to  glass.  These 
snow  huts  are  carefully  built,  as  pointed  out  by 
Woeikof ,  not  of  freshly-fallen  snow,  but  of  snow  well- 
compacted  by  successive  storms  and  winds.  The 
snow  becomes  dense  by  this  means,  and  not  by  being 
successively  melted  and  frozen,  as  in  a  neve.  In 
the  drier  parts  of  Greenland,  simple  earth  or  stone 
houses  are  also  used,  and  in  the  larger  towns  wooden 
houses,  built  of  imported  lumber,  are  the  ordinary 
residences  of  the  inhabitants.  The  snow  igloo  is  the 
common  type  of  the  more  permanent  winter  dwell- 
ing. In  summer,  when  these  huts  may  be  damp 
with  melting  snow,  the  nomadic  Eskimo  travels  with 
tents  made  of  skins,  sewed  with  animal  sinews  or 
strips  of  leather,  and  set  up  with  tusks  or  bones. 
Settlements,  established  during  wanderings  in  search 
of  good  hunting  and  fishing  grounds,  may  fre- 


LIFE  OF  MAN  IN  POLAR  ZONES  333 

quently  be  occupied  and  abandoned  several  times,  and 
the  ruins  of  abandoned  settlements  north  of  the 
present  limits  of  human  habitations  may  probably 
often  be  thus  explained.  Even  in  winter,  if  the 
food  supply  gives  out,  changes  of  residence  are  not 
uncommon. 

Food  and  Clothing.  The  clothing  of  the  Eskimo 
is  made  of  skins  of  the  reindeer,  seal,  or  bear,  or  of 
birds,  worn  almost  in  their  natural  state.  As  a  pro- 
tection against  the  cold,  the  face  is  often  smeared 
with  fat.  Food  consists  chiefly,  or  wholly,  of  heat- 
producing  materials,  such  as  bear  or  seal  meat,  and 
blubber  from  seal,  walrus,  or  whale,  eaten  raw  or 
barely  heated  through.  Any  surplus  food  is  usually 
well  preserved  by  the  cold. 

Travel  and  Transportation.  The  need  of  quick 
travel,  over  great  distances  on  land,  in  search  of  food, 
makes  the  dog-sledge  an  indispensable  possession  of 
the  Eskimo.  The  dog,  living  on  animal  food,  can 
travel  farther  north  than  the  reindeer,  and  is  the  typi- 
cal polar  draught-animal  beyond  the  reindeer  coun- 
try. The  dog-sledge  has  spread  the  Eskimo  far  and 
wide  over  the  Arctic  zone.  Conditions  are  not  always 
equally  favourable  for  sledging.  Sometimes  the 
runners  are  covered  with  ice  to  make  them  smoother 
and  to  prevent  their  sinking  into  the  snow.  In  Lab- 
rador, the  winter  storms  which  sweep  off  the  loose 
snow  and  leave  the  surface  hard  and  smooth  are  wel- 
comed as  giving  the  best  conditions  for  sledging. 

Occupations    and    Arts.     Hunting    and    fishing, 


334  CLIMATE 

training  the  dogs,  and  making  kayaks,  sledges,  weap- 
ons, and  utensils  are  the  chief  occupations  of  the  men, 
while  the  women  make  the  clothing  and  chew  the 
skins    to    soften    them.     The    Eskimo    displays    the 
greatest  mechanical  skill  and  ingenuity  in  fashioning 
all  his  tools  and  utensils.     As  trees  do  not  grow  in  his 
country,  wood  is   so  scarce  that  every  bit  of  it  is  used, 
small  pieces  even  being  bound  together  with  leathern 
thongs  to  make  the  handles  of  knives  and  harpoons, 
and  the  like.     Every  piece  of  driftwood  is  a  precious 
possession,  more  valuable  often  than  iron.      Drift- 
wood plays  an  important  part  in  the  history  and  laws 
of  Iceland,  and  Nansen  says  that  the  driftwood  "  car- 
ried down  by  the  polar  current  along  the  east  coast  of 
Greenland  and  up  the  west  coast  is    ...    essential 
to  the  existence  of  the  Greenland  Eskimo."     Wood 
and  iron  are  used  instead  of  bone  and  skins.     The 
utensils  of  Arctic  natives  show  at  once  whether  or  not 
they  have  had  access  to  supplies  of  driftwood.  It  has 
been  well  said  that  where  driftwood  is  found  undis- 
turbed this  is  good  evidence  that  there  are  no  Eski- 
mos in  the  vicinity.      The  distribution  of  man  thus 
depends  largely  on  the  course  taken  by  the  driftwood. 
The  skill  of  the  Eskimo  is  well  shown  in  his  construc- 
tion of  the  kayak;  made  of  skins  sewn  together  and 
stretched  over  a  framework,  a  marvel  of  lightness,  in- 
destructibility, and  portability,  easily  righted  if  over- 
turned, which  fits  the  boatman  as  if  he  and  his  boat 
were  one.     Needles  and  thimbles  are  made  of  bone; 
animal  fibres  are  used  for  thread ;  narwhal  tusks  serve 


LIFE  OF  MAN  IN  POLAR  ZONES  335 

as  tent-pegs.  The  Eskimo  can  make  or  mend  any- 
thing that  he  uses.  Nothing  is  wasted.  The  Eski- 
mos are  naturally  expert  sailors,  because  of  their  life 
on  the  sea.  In  towing  their  catches  to  land,  they 
make  use  of  inflated  bladders  or  skins. 

Customs.  The  lack  of  water,  and  the  cold,  com- 
bine to  make  personal  cleanliness  difficult,  and  the 
people  are  characteristically  very  dirty.  The  winter, 
when  the  Eskimos  are  living  in  their  more  permanent 
huts,  is  the  time  for  social  visiting,  and  then  they 
travel  for  miles  in  the  family  sledges  to  visit  their 
friends.  Marriages  take  place  at  an  early  age, 
especially  among  the  women,  and  the  return  of  the 
sun  after  the  long  winter  has  a  stimulating  effect  on 
the  animal  passions  which  leads  to  sexual  excesses  of 
all  kinds.1 

Deserts  of  Sand  and  Deserts  of  Snow.  The  hot 
deserts  of  sand  near  the  equator  and  the  frozen  des- 
erts of  snow  near  the  pole  are  singularly  alike  in  many 
ways  in  relation  to  man.  Both  alike  repel  him.  Both 
are  largely  or  wholly  destitute  of  vegetation,  of  wood, 
and  of  water.  The  grey  or  yellow  desolate  waste  of 
the  sand  desert  is  matched  by  the  monotonous  white 
surface  of  the  snow  desert.  There  are  no  opportuni- 
ties for  accumulating  wealth  in  either.  Travel  is  dif- 
ficult in  both.  In  one,  the  camel  is  the  typical  beast 
of  burden;  in  the  other,  the  reindeer  and  the  dog  are 
man's  most  useful  possessions.  The  monotonous 

'"Some  Physiological  Effects  of  Arctic  Cold,  Darkness  and  Light/' 
Med.  Rec.,  June  12,  1897,  pp.  833-836. 


336  CLIMATE 

heat  and  glare  and  silence  of  the  sand  desert  find  their 
counterpart  in  the  cold  and  glare  and  silence  of  the 
snow  desert.  The  air  is  generally  clear  in  both,  ex- 
cept for  the  dust  over  the  sand  desert  and  the  ice- 
needles  in  the  air  of  the  snow  desert.  In  both  deserts 
man  in  very  limited  in  his  food  supply;  in  the  Sahara, 
the  date,  and  in  Greenland,  the  seal,  are  typical  staple 
articles  of  diet.  The  aridity  in  one,  the  cold  in  the 
other,  are  man's  great  enemies.  The  inhabitants  of 
both  deserts  are  nomadic.  Settlements  of  some  per- 
manency are  found  in  oases  or  along  the  edges  of  the 
sand  desert  where  there  is  water ;  similarly,  the  natives 
of  the  far  north  live  along  the  edges  of  the  ice 
desert,  where  they  can  best  find  their  food.  The 
sand  deserts  are  deserts  because  they  are  arid.  The 
snow  deserts  are  deserts  because  they  are  cold. 
Denudation  of  exposed  rocks  in  both  types  of  desert 
is  largely  due  to  the  action  of  wind,  for  running 
water  is  seldom  found.  The  dust  of  disintegration 
is  carried  away  by  the  winds,  and  sand-blasting  has 
been  reported  of  the  antarctic  desert  as  well  as  of 
the  Sahara.  The  polar  deserts  are  perhaps  on  the 
whole  better  suited  to  life  than  the  sand  deserts,  for 
the  former  do  supply  water  from  melted  snow  and 
ice,  and  over  the  tundra  portion  of  the  frozen  desert 
there  is  an  abundance  of  water  in  the  rivers  in  sum- 
mer, with  moss,  berries,  and  other  vegetation,  as  well 
as  animal  food.  Man  has,  however,  a  harder  strug- 
gle to  protect  himself  against  the  cold  than  against 
the  heat,  for  he  needs  more  clothing,  and  better  shel- 


LIFE  OF  MAN  IN  POLAR  ZONES  337 

ter,  and  fire.  In  both  deserts  life  is  isolated  and 
primitive.  The  sand  desert  is  crossed  by  caravans 
and  trade  routes  between  the  more  populous  lands  on 
either  side,  and  the  people  of  these  deserts  have  more 
contact  with  civilisation  than  do  most  of  the  natives 
of  the  far  north. 


CHAPTER  XI 

CHANGES  OF  CLIMATE 

Popular  Belief  in  Climatic  Change — Evidence  of  Climatic  Changes 
Within  Historic  Times — What  Meteorological  Records  Show 
—Why  the  Popular  Belief  in  Climatic  Changes  is  Untrust- 
worthy— Value  of  Evidence  Concerning  Changes  of  Climate — 
Periodic  Oscillations  of  Climate:  The  Sun-spot  Period Bruck- 
ner's 35-Year  Cycle — Climatic  Cycles  of  Longer  Period — 
Geological  Changes  in  Climate — Conclusion. 

Popular  Belief  in  Climatic  Change.  Belief  in  a 
change  in  the  climate  of  one's  place  of  residence, 
within  a  few  generations,  and  even  within  the  mem- 
ory of  living  men,  is  widespread.  It  is  confined  to 
no  special  region  or  people.  It  finds  support  among 
the  most  intelligent  as  well  as"  among  the  uneducated. 
Here  it  may  be  the  view  that  the  climate  is  growing 
milder;  there,  that  the  winters  are  becoming  more 
severe;  here,  that  there  is  increasing  aridity;  there, 
that  the  rainfall  is  greater.  Whenever  a  season 
attracts  attention  because  of  weather  conditions 
which  seem  in  any  way  unusual,  this  belief  is 
strengthened.  This  popular  impression  has  often 
found  support  in  the  facts  of  distribution,  or  the 
dates  of  flowering,  or  ripening,  of  certain  cereals  or 
fruits.  It  is  asserted  that  because  grapes,  or  corn, 

33$ 


CHANGES  OF  CLIMATE  339 

or  olives,  for  example,  are  now  no  longer  grown  in 
parts  of  Europe  where  their  cultivation  was  once  an 
important  occupation,  we  must  conclude  that  the 
climate  has  changed  from  a  favourable  to  an  un- 
favourable one. 

Evidences  of  Climatic  Changes  within  Historic  Times. 
Evidence  is  constantly  being  brought  forward  of 
apparent  climatic  variations  of  greater  or  less  amount 
which  have  occurred  during  historic  times,  and  some 
of  which  seem  now  to  be  going  on.  Such  reports, 
largely  those  of  travellers  or  explorers  in  compara- 
tively little-known  regions,  are  based  on  fluctuations 
in  the  extent  of  inland  lakes;  on  the  discovery  of 
abandoned  dwelling  sites,  the  ruins  of  aqueducts  and 
irrigating  canals,  and  of  human  utensils  and  imple- 
ments; as  well  as  on  the  study  of  strand  lines,  dunes, 
river  terraces,  abandoned  river  channels,  vegetation, 
the  salinity  of  lakes,  desert  roads  now  too  dry  for 
caravans,  and  the  like.  In  several  cases  descrip- 
tions have  been  given  of  extended  ruins  showing 
human  occupation  by  a  former  large  population  in 
districts  where  there  now  seems  to  be  an  absolutely 
insufficient  water-supply,  or  where  the  waters  arc 
too  saline  for  use.  Thus  we  have  many  accounts, 
based  on  various  lines  of  evidence  similar  to  that  just 
referred  to,  of  a  gradual  desiccation  which  seems  to 
have  been  going  on  over  a  large  region  in  central 
Asia  during  historical  times. 

In  northern  Africa,  certain  ancient  historical  re- 
cords have  been  taken  by  different  writers  to  indicate 


340  CLIMATE 

a  general  decrease  of  rainfall  during  the  last  3000 
years  or  more,  the  remains  of  cities  and  the  ruins  of 
irrigating  works  pointing  to  a  larger  population  and 
a  greater  water  supply  formerly  than  at  present. 
The  presence  of  certain  animals,  now  no  longer  found 
there,  is  implied  by  ancient  records  and  pictographs, 
and  from  this  fact,  as  well  as  from  a  study  of  the  past 
and  present  flora  of  the  region,  and  of  its  river  history 
also,  a  change  from  a  moister  to  a  drier  climate  is 
inferred.  From  the  Sahara,  evidence  of  a  former 
large  population  has  been  adduced  and  a  gradual 
desiccation  of  that  region  is,  therefore,  believed 
to  have  taken  place.  Recently,  however,  the  equa- 
torial rain-belt  seems  to  have  been  advancing  farther 
north,  giving  an  increased  rainfall.  Gautier  has 
divided  the  history  here  into  three  periods:  (1) 
dense  population;  (2)  aridity;  and  (3)  the  present 
change  to  steppe  character. 

Farther  south,  several  lakes  have  been  reported  as 
decreasing  in  size,  and  wells  and  springs  as  running 
dry.  In  the  Lake  Chad  district,  Chevalier  has 
reported  the  discovery  of  vegetable  and  animal 
remains  which  indicate  an  invasion  of  the  Sudan  by  a 
Saharan  climate.  Neolithic  relics  indicate  the  former 
presence  there  of  prosperous  communities.  Again, 
many  writers  hold  that  a  decrease  in  rainfall  has 
taken  place  within  historic  times  over  Greece,  Syria, 
and  other  eastern  Mediterranean  lands,  as  well  as  in 
Italy  and  other  countries  over  the  western  portion 
of  the  Mediterranean.  These  examples  might  be 


CHANGES  OF  CLIMATE  341 

multiplied,  for  reports  of  climatic  changes  of  one 
kind  or  another  are  numerous  from  many  parts  of  the 
globe.  The  literature  on  the  subject  is  already  very 
extended  and  relates  to  many  different  parts  of 
the  world,  including  southern  as  well  as  northern 
Africa,  Australia,  south-western  North  America, 
Central  America,  and  several  of  the  more  arid  dis- 
tricts of  South  America,  where  the  recent  investiga- 
tions of  Bowman  seem  to  confirm  the  views  of 
progressive  desiccation  previously  expressed  by 
several  others.  As  a  whole,  the  general  impression 
which  the  reader  gains  from  a  study  of  much  of  this 
literature  is  that  of  a  widespread  tendency  toward 
increasing  aridity.  There  are,  however  many  excel- 
lent authorities  who  do  not  unqualifiedly  accept  the 
evidence  thus  far  brought  forward,  and  who  take  the 
opposite  view,  or  at  least  regard  the  matter  as  still 
far  from  being  definitely  settled. 

Dr.  Ellsworth  Huntington  has  contributed  largely 
to  the  discussion  regarding  variations  of  climate 
within  historic  times.  Beginning  his  investigations 
in  Asia, — in  Turkestan,  Transcaspia,  and  Persia, — he 
has  extended  his  studies  to  include  Palestine  and  the 
Libyan  Desert,  and,  more  recently,  the  more  arid 
portions  of  North  America,  Central  and  South 
America.  His  evidence  is  derived  from  the  ar- 
chaeology, physiography,  botany,  history,  and  tradi- 
tion of  the  areas  under  discussion.  The  various 
kinds  of  evidence  are  matched,  and  are  found  by 
him  to  accord  in  a  striking  manner.  Huntington's 


342  CLIMATE 

latest  work,  in  western  North  America,  includes 
an  examination  of  the  rings  of  the  big  trees  of 
California,  which  are  believed,  to  furnish  accurate 
gauges  of  the  climatic  variations  which  have  taken 
place  during  their  long  period  of  life.(  The  general 
conclusion  drawn  from  a  study  of  this  great  body  of 
evidence  is  that  the  main  climatic  variations  were 
synchronous  in  the  Mediterranean  regions,  in  Central 
Asia,  and  in  North  and  Central  America;  that  from 
the  dawn  of  human  history  there  has  been  a  general 
change  from  moister,  and  presumably  cooler,  to 
drier  and  warmer  climates.  This  change  has  not 
gone  on  uniformly,  but  has  taken  place  more  or  less 
irregularly,  in  a  pulsatory  fashion,  drier  and  moister 
periods  alternating  with  one  another.^ 

These  climatic  "pulsations"  are  correlated  with 
certain  important  historic  events,  such  as  the  decline 
of  Persia,  agrarian  troubles  in  Rome,  barbarian 
invasions,  and  the  decline  and  subsequent  revival  of 
civilization  in  Central  America.  A  "remarkable 
agreement"  has  been  found  between  these  historic 
events  and  the  "apparent  climatic  changes."  The 
latter  "seem  competent  to  give  rise  to  the  observed 
results."  Dr.  Huntington  has  plotted  curves  show- 
ing variations  in  the  rapidity  of  growth  of  the  "big 
trees"  of  California  since  1300  B.C.,  and  these  curves, 
in  his  judgment,  are  in  substantial  agreement  with 
his  climatic  curves  for  central  and  western  Asia. 
Hence  the  conclusion  that,  in  similar  latitudes  of 
western  Asia  and  of  western  North  America,  I  lie 


CHANGES  OF  CLIMATE  343 

pulsations  of  climate  were  essentially  synchronous 
and  of  the  same  character. 

What  Meteorological  Records  Show.  As  concerns 
the  popular  impression  regarding  change  of  climate, 
it  is  clear  at  the  start  that  no  definite  answer  can  be 
given  on  the  basis  of  tradition,  or  of  general  impres- 
sion, or  even  of  the  memory  of  the  "  oldest  inhabi- 
tant." Human  memories  are  very  untrustworthy, 
and  there  are  many  reasons  for  their  being  particu- 
larly untrustworthy  in  matters  of  this  kind.  The  only 
answer  of  real  value  must  be  based  on  what  the  in- 
strumental records  of  temperature,  and  of  rain  and 
snowfall  show.  Accurate  instruments,  properly  ex- 
posed and  carefully  read,  do  not  lie;  do  not  forget; 
are  not  prejudiced.  When  such  instrumental  records, 
scattered  though  they  are,  and  difficult  as  it  is  to 
draw  general  conclusions  from  them,  are  carefully 
examined,  from  the  time  when  they  were  first  kept, 
which  in  a  few  cases  goes  back  about  one  hundred  and 
fifty  years,  there  is  found  no  evidence  of  any  progres- 
sive change  in  temperature,  or  in  the  amount  of  rain 
and  snow.  '  Apparent  signs  of  a  permanent  increase 
or  decrease  in  one  or  another  element  have  been  fairly 
easy  to  explain  as  due  to  the  method  of  exposing  the 
thermometer,  or  of  setting  up  the  rain-gauge.  Little 
care  was  formerly  taken  in  the  construction  and  loca 
tion  of  meteorological  instruments.  They  were  usu- 
ally in  cities,  and  as  these  cities  grew,  the  temperature 
of  the  air  was  somewhat  affected.  The  rain-gauges 
were  poorly  exposed  on  roofs  or  in  court-yards.  The 


314  CLIMATE 

building  of  a  fence  or  a  wall  near  the  thermometer, 
or  the  growth  of  a  tree  over  a  rain-gauge,  is 
enough,  in  many  cases,  to  explain  any  observed 
change  in  the  mean  temperature  or  rainfall.  Even 
when  the  most  accurate  instrumental  records  are 
available,  care  must  be  taken  to  interpret  them  cor- 
rectly. Thus,  if  a  rainfall  or  snowfall  record  of  sev- 
eral years  at  some  station  indicates  an  apparent 
increase  or  decrease  in  the  amount  of  precipitation, 
it  does  not  necessarily  follow  that  this  means  a  per- 
manent, progressive  change  in  climate,  which  is  to 
continue  indefinitely.  It  may  mean  simply  that  there 
have  been  a  few  years  of  somewhat  more  precipita- 
tion, and  that  a  period  of  somewhat  less  precipitation 
is  to  follow. 

For  the  United  States,  Schott,  some  thirty  years 
ago,  made  a  careful  study  of  all  the  older  records  of 
temperature  and  rainfall,  including  snow,  from  Maine 
to  California,  and  found  nothing  which  led  to  the  view 
of  a  progressive  change  in  any  one  direction,  but  it 
did  appear  that  waves  of  higher  and  lower  temperature 
followed  one  another  at  intervals  of  about  twenty- 
two  years  on  the  Atlantic  coast.  In  the  interior, 
the  intervals  were  about  seven  years.  The  earliest 
known  measurements  of  rainfall  were  made  in  Pales- 
tine, in  the  first  century  A.D.,  and  the  results  were 
preserved  in  the  Mishnah,  a  collection  of  Jewish 
religious  books.  A  comparison  of  these  early  obser- 
vations with  those  of  the  present  shows  that  there 
has  been  no  change  in  the  climate  of  Palestine. 


CHANGES  OF  CLIMATE  345 

ft 

Non-instrumental  records,  both  regular  and  oc- 
casional, of  the  opening  and  closing  of  rivers  to 
navigation,  of  severe  winters,  etc.,  in  Europe,  in  some 
cases  go  back  several  centuries,  but  give  no  evidence 
of  any  progressive  change  in  climate  there.  The 
records  of  the  closing  of  the  Hudson  to  navigation 
show  no  permanent  change  in  the  dates  for  the  last 
hundred  years  or  so.  It  has  been  well  pointed  out 
that  if  a  list  were  carefully  compiled  of  heavy  snow- 
storms, of  droughts,  of  floods,  of  severe  cold,  of  mild 
winters,  of  heavy  rains,  and  of  other  similar  meteoro- 
logical phenomena,  for  one  of  the  early-settled  sec- 
tions of  the  United  States,  beginning  with  the  date  of 
the  first  white  settlements  and  extending  down  to  the 
present  day,  we  should  have  the  following  situation : 
Dividing  this  list  into  halves,  each  division  con- 
taining an  equal  number  of  years,  it  would  be  found, 
speaking  in  general  terms,  that  for  every  mild  winter 
in  the  first  half,  there  would  be  a  mild  winter  in  the 
second;  for  every  long-continued  drought  in  the  first 
division,  there  would  be  a  similar  drought  in  the 
second;  for  every  "old-fashioned"  winter  in  the  first 
group,  there  would  be  an  (( old-fashioned"  winter  in 
the  second.  And  so  on,  through  the  list.  In  other 
words,  weather  and  climate  have  not  changed  from 
the  time  of  the  landing  of  the  earliest  pilgrims  down 
to  the  present  day. 

Popular    Belief    in    Climatic    Changes     Untrust-  ' 
worthy.     Why   is    the   popular    belief   in   a   change 
of    climate    so    widespread    and    so    firmly    fixed, 


346  CLIMATE 

when  instrumental  records  all  go  to  show  that  this 
belief  is  erroneous?  It  is  not  easy  to  answer  this 
question  satisfactorily,  but  several  possible  explana- 
tions may  be  given.  The  trouble  arises  chiefly  from 
the  fact  that  we  place  absolute  trust  in  our  memories, 
and  attempt  to  judge  such  subtle  things  as  climatic 
changes  on  the  basis  of  these  memories,  which  are  at 
best  short,  defective,  and  in  the  highest  degree  un- 
trustworthy. We  are  likely  to  exaggerate  past 
events;  to  remember  a  few  exceptional  seasons  which, 
for  one  reason  or  another,  made  a  deep  impression 
on  us,  and  we  thus  very  much  overrate  some  special 
event.  To  make  use  of  an  illustration  given  by  an- 
other, individual  severe  winters  which,  as  they  occur, 
may  be  some  years  apart,  seem,  when  looked  back 
upon  from  a  distance  of  several  years  later,  to  have 
been  close  together.  It  is  much  as  in  the  case  of  the 
telegraph  poles  along  a  railroad  track.  When  we 
are  near  the  individual  poles,  they  seem  fairly  far 
apart,  but  when  we  look  down  the  track,  the  poles 
seem  to  stand  close  together.  The  difference  in  the 
impressions  made  upon  youthful  and  adult  minds 
may  account  for  part  of  this  misconception  regard- 
ing changes  of  climate.  To  a  youthful  mind  a  heavy 
snowstorm  is  a  memorable  thing.  It  makes  a  deep 
impression,  which  lasts  long  and  which,  in  later  years, 
when  snowstorms  are  just  as  heavy,  seems  to  dwarf 
the  recent  storms  in  comparison  writh  the  older.  The 
same  is  true  regarding  heavy  rains,  or  floods,  or 
droughts. 


CHANGES  OF  CLIMATE  347 

^  Changes  of  residence  may  account  for  some  of  the 
prevailing  ideas  about  climate.  One  who  was 
brought  up  as  a  child  in  the  country,  where  snow 
drifts  deep  and  where  roads  are  not  quickly  broken 
out,  and  who  later  removes  to  a  city,  where  the  tem- 
peratures are  slightly  higher,  where  the  houses  are 
warmer,  and  where  the  snow  is  quickly  removed  from 
the  streets,  naturally  thinks  that  the  winters  are 
milder  and  less  snowy  than  when  he  was  a  boy. 
Similarly,  a  change  of  residence  from  a  hill  to  a  val- 
ley, or  vice  versa,,  or  from  the  coast  to  the  interior, 
may  easily  give  the  impression  of  a  changing  climate. 
Even  in  cases  where  individuals  have  kept  a  record  of 
thermometer  readings  during  a  long  series  of  years, 
and  are  sure  that  the  temperatures  are  not  as  low 
or  as  high  as  they  used  to  be,  or  who  are  convinced 
(hat  the  rainfall  is  lighter  or  heavier  than  it  was 
some  years  before,  the  chances  are  that  the  location 
of  the  thermometer,  or  the  exposure  of  the  rain  gauge, 
has  been  changed  sufficiency  to  account  for  any 
observed  difference  in  the  readings. 

Value  of  Evidence  Concerning  Changes  of  Climate. 
There  are  certain  considerations  which  should  be 
borne  in  mind  in  dealing  with  the  evidence  of  changes 
of  climate  within  historic  times;  certain  corrections, 
so  to  speak,  which  should  be  made  for  possible  con- 
trols other  tjian  climatic,  before  definite  conclusions 
are  reached  in  favour  of  climatic  changes. 

In  the  first  place,  there  is  a  large  body  of  facts  con- 
cerning the  past  and  present  conditions  of  cultivated 


348  CLIMATE 

crops,  and  of  vegetation  in  general.  It  has  been 
noted  above  that  changes  in  the  distribution  of  certain 
fruits  and  cereals,  and  in  the  dates  of  the  harvest, 
have  often  been  accepted  as  undoubted  evidence 
of  changes  in  climate.  Such  a  conclusion  is  by  no 
means  inevitable,  for  it  can  easily  be  shown  that  many 
changes  in  the  districts  of  cultivation  of  various 
crops  naturally  result  from  the  fact  that  grapes,  or 
corn,  or  olives,  are  in  time  found  to  be  more  pro- 
fitably grown,  or  more  easily  prepared  for  market 
in  another  locality.  In  other  words,  economic,  and 
not  climatic,  controls,  may  often  be  the  determining 
factor.  Thus  the  area  covered  by  vineyards  in 
northern  Europe  has  been  very  much  restricted  in  the 
last  few  hundred  years,  because  grapes  can  be  raised 
better  and  cheaper  farther  south.  |  Cultivation  in  one 
district  is  abandoned  when  it  is  more  profitable  to  im- 
port the  product  from  another.  It  is  easy,  but  not 
right,  to  conclude  that  the  climate  of  the  districts  first 
used  has  changed.  Wheat  was  formerly  more  gen- 
erally cultivated  far  north  in  the  British  Isles  than  is 
the  case  at  present,  because  it  was  profitable.  Later, 
after  a  readjustment  of  the  taxes  on  breadstuff s,  it 
was  no  longer  profitable  to  grow  cereals  in  that 
region,  and  the  area  thus  cultivated  diminished. 
Changes  in  the  facility,  or  in  the  cost,  of  importation 
of  certain  articles  of  food  from  a  distance  are  speedily 
followed  by  changes  in  the  districts  over  which  these 
same  crops  are  grown.  Similarly,  the  introduction  of 
some  new  plant,  better  suited  to  the  local  soil  and 


CHANGES  OF  CLIMATE  349 

climate,  will  result  in  the  replacement  of  the  older  pro- 
duct by  the  newer.  In  France,  Angot  has  made  a 
careful  compilation  of  the  dates  of  the  vintage  from 
the  fourteenth  century  down  to  the  present  time,  and 
finds  no  support  for  the  view  so  commonly  held  there 
that  the  climate  has  changed  for  the  worse.  The  dates 
of  the  vintage  do,  however,  indicate  some  oscillation 
of  the  climatic  elements.  In  the  period  1775-1875, 
the  average  date  of  the  grape  harvest  in  Aubonne  was 
about  ten  days  earlier  than  during  the  preceding  cen- 
tury, but  three  days  later  than  during  the  second 
century  preceding.  At  the  present  time,  the  average 
date  of  the  grape  harvest  in  Aubonne  is  exactly  the 
same  as  at  the  close  of  the  sixteenth  century.  After 
a  careful  study  of  the  conditions  of  the  date  tree, 
from  the  fourth  century  B.C.,  Eginitis  concludes  that 
the  climate  of  the  eastern  portion  of  the  Mediterran- 
ean basin  has  not  changed  appreciably  during 
twenty-three  centuries.  A  careful  examination  of  the 
writings  of  Homer,  Hesiod,  Aristotle,  Theophrastus, 
Strabo,  and  other  ancient  classic  authors,  has  led 
several  recent  students  of  this  question  to  the  definite 
conclusion  that  no  appreciable  climatic  change  has 
taken  place  in  the  Mediterranean  region  within  the 
last  thirty  centuries.  Lately,  Hildebrandsson  has 
again  reviewed  the  botanical  evidence  from  Palestine, 
and  finds  that  the  culture  of  the  vine  and  the  date 
indicates  the  same  climatic  conditions  now  as  for- 
merly. In  Italy,  too,  the  laurel,  the  myrtle,  and  the 
fir  are  growing  now  where  they  grew  in  the  days  of 


3.50  CLIMATE 

Pliny  and  Virgil.  Arago,  in  his  time,  concluded 
that  there  had  been  no  change  in  Palestine  in  three 
thousand  years.  In  China,  a  comparison  of  the 
ancient  and  present-day  conditions  of  cultivation, 
of  silk  production,  and  of  bird  migrations,  has  led 
Biot  to  a  similar  conclusion.  To  this  evidence, 
derived  from  the  past  and  present  distribution  of 
vegetation,  those  who  believe  in  climatic  change 
object  on  the  ground  that  at  the  height  of  the  last 
glacial  epoch  the  mean  temperature  of  the  earth  was 
probably  only  about  10°  or  at  most  20°,  cooler  than 
now.  On  that  basis,  an  historic  change  a  tenth 
as  great  as  the  enormous  change  since  the  height 
of  glaciation  would  mean  a  temperature  change  too 
small  to  detect  by  means  of  vegetation. 

Again,  in  some  cases,  the  reported  cultivation  of 
cereals,  or  other  soil  products,  in  certain  climates  at 
present  unfavourable,  has  been  shown  to  be  purely 
a  myth;  as  in  the  case  of  Greenland  and  of  Iceland. 
Thoroddsen,  the  leading  authority  on  Iceland,  has 
shown  that  political  and  economic  changes  amply 
suffice  to  account  for  all  changes  in  crop  cultivation 
in  that  country. 

The  evidence  derived  from  a  study  of  the  "big 
tree"  rings  in  California  has  not  been  unchallenged. 
Seasonal,  rather  than  annual,  rainfall,  and  other 
factors  such  as  temperature,  insect  pests,  the  height 
of  the  surrounding  trees,  etc.,  are  controls  which 
enter  in  to  complicate  the  problem,  and  make  it 
difficult  to  draw  definite  conclusions  regarding  the 


CHANGES  OF  CLIMATE  351 

climates  of  the  past.  On  the  other  hand,  those 
who  accept  the  evidence  of  the  tree  rings  reply  that 
in  our  own  day  exact  records  show  an  unmistakable 
harmony  between  spring  rainfall  and  tree  growth 
in  California,  on  the  one  hand,  and  Mediterranean 
rainfall  on  the  other.  Hence,  they  maintain,  it 
seems  legitimate  to  infer  that  the  main  fluctuations 
in  tree  growth  represent  climatic  pulsations  of  almost 
world -wide  extent. 

Secondly,  many  of  the  reports  by  explorers  from 
little-known  regions  are  extraordinarily  contradictory. 
Thus  Lake  Aral,  which  was  diminishing  in  area  f  or  '  ' 
many  years,  has  recently  been  reported  by  Berg  to  •' 
be  increasing.  A  railroad  built  along  the  shores  of 
this  lake  has  been  moved  because  of  the  encroachment 
of  the  waters  upon  the  road  bed.  Lake  Balkash, 
which  was  rapidly  drying  up,  has  also  begun  to  fill 
again.  Partly  submerged  trees  are  noted  as  having 
been  seen  by  Berg,  who  in  June,  1902,  found  the  lake 
waters  quite  fresh.  As  the  lake  has  no  outlet,  this 
is  an  interesting  fact.  Woeikof,  in  his  last  study 
of  the  Turkestan  region,  reported  increasing  rainfall 
and  expanding  and  deepening  lakes,  and  opposed  the 
view  of  a  general  desiccation.  Stein  (1907)  reported 
a  distinct  extension  of  the  cultivated  area  as  having 
taken  place  in  Khotan  between  the  times  of  his  last 
two  visits  to /that  region.  In  Africa,  Lake  Victoria, 
which,  it  was  generally  agreed,  was  sinking  in  the 
period  1878-1892,  has  since  shown  a  tendency  to  rise. 
Lake  Rukwa,  east  of  Tanganyika,  has  risen  within 


352  CLIMATE 

the  last  few  years.  Lake  Chad  is  very  probably 
subject  to  oscillations,  sometimes  spreading  beyond 
its  usual  limits  as  the  result  of  several  years  of 
heavy  rainfall.  Such  diverse  reports  show  the  need 
of  caution  in  jumping  at  conclusions  of  climatic 
change.  An  increased  use  of  water  for  irrigation 
may  cause  the  level  of  water  in  a  lake  to  fall,  as  has 
been  the  case  to  some  extent  in  Great  Salt  Lake. 
Periodic  oscillations,  giving  higher  and  then  lower 
water,  do  not  indicate  progressive  change  in  one  di- 
rection. Many  writers  have  thus  seen  a  law  in  what 
was  really  a  chance  coincidence.  Partsch  believes 
that  the  ancient  settlements  on  the  interior  lakes  of 
northern  Africa  show  that  these  lakes  contained  no 
more  water  formerly  than  they  do  now.  Some  have 
claimed  that  the  supposed  desiccation  of  the  climate 
of  northern  Africa  resulted  from  deforestation,  but 
no  certain  evidence  exists  of  the  presence  or  destruc- 
tion of  such  forests,  and  if  deforestation  did  take 
place,  no  considerable  change  of  climate  could  have 
resulted. 

Thirdly,  where  a  progressive  desiccation  seems  to 
have  taken  place,  the  question  should  be  asked,  Is  less 
rain  actually  falling,  or  have  the  inhabitants  less 
capacity,  less  energy,  less  ability,  than  formerly?  Is 
the  change  from  a  once  cultivated  area  to  a  barren 
expanse  the  result  of  decreasing  rainfall,  or  of  the 
emigration  of  the  former  inhabitants  to  other  lands? 
The  difference  between  a  country  formerly  well  irri- 
gated and  fertile,  and  a  present-day,  sandy,  inhospit- 


CHANGES  OF  CLIMATE  353 

able  waste  may  be  the  result  of  a  former  compulsion 
of  the  people,  by  a  strong  governing  power,  to  till 
the  soil  and  to  irrigate,  while  now,  without  that  com- 
pulsion, no  attempt  is  made  to  keep  up  the  work. 
The  incapacity  of  the  present  inhabitants,  or  of  their 
rulers,  is  often  responsible  for  effects  which  have  been 
interpreted  as  due  to  climatic  change.  Where  irri- 
gation is  now  being  again  resorted  to  in  parts  of  the 
districts  about  the  Mediterranean  which  have  been 
reported  to  be  drying  up,  there  the  former  fruitful- 
ness  is  returning.  In  Asia  Minor,  for  example,  the 
rule  of  the  Turk  brought  a  change  from  a  settled 
and  civilised  to  a  semi-nomadic  state  of  society;  in- 
dustries died  out,  the  land  to  a  great  extent  passed 
out  of  cultivation;  irrigation  works  were  destroyed. 
Recently  the  building  of  railroads  and  of  roads  has 
been  followed  by  a  revival  of  industry  and  of  agricul- 
ture, and  by  the  reclamation  of  waste  land.  In  many 
cases  the  reports  of  increasing  dryness  really  concern 
only  the  decrease  in  the  water  supply  from  rivers 
and  springs,  and  it  is  well  known  that  a  change  in  the 
cultivation  of  the  soil,  or  in  the  extent  of  the  forests, 
may  bring  about  marked  changes  in  the  flow  of 
springs  and  rivers  without  any  essential  change  in 
the  actual  amount  of  rainfall.  These  conditions  are 
particularly  likely  to  occur  in  regions  where  there  is 
no  snow  covering,  and  where  the  rain  falls  in  a  few 
months  only.  In  Tripoli,  the  Vicomte  de  Mathui- 
sieulx  finds  that  the  Latin  texts  and  monuments 
seem  to  establish  the  fact  that,  so  far  as  atmospheric 

33 


354  CLIMATE 

conditions  and  soil  are  concerned,  everything  is  just 
as  it  was  in  ancient  times.  The  present  condition  of 
the  country  is  ascribed  to  the  idleness  of  the  Arabs, 
who  have  allowed  wells  to  become  choked  and  vegeta- 
tion to  perish.  "  In  a  country  so  little  favoured  by 
nature,  the  first  requisite  is  a  diligent  and  hard-work- 
ing population.  The  Romans  took  several  centuries 
to  make  the  land  productive  by  damming  rivers  and 
sinking  wrells  in  the  wady  beds."  In  an  arid  region, 
man  has  a  hard  task  if  he  is  to  overcome  the  climatic 
difficulties  of  his  situation.  Irrigation ;  the  choice  of 
suitable  crops  adapted  to  arid  conditions;  steady, 
thoughtful  work,  are  absolutely  essential.  To  a  large 
extent,  an  intelligent  man  may  thus  overcome  many 
of  the  obstacles  which  nature  has  put  in  his  way.  On 
the  other  hand,  a  region  of  deficient  rainfall,  once 
thickly  settled  and  prosperous,  may  readily  become 
an  apparently  hopeless  desert,  even  without  the  in- 
tervention of  wrar  and  pestilence,  if  man  allows  the 
climate  to  master  him.  A  change  in  man  doubtless 
explains  many  of  the  facts  which  have  been  brought 
forward  as  evidences  of  a  change  in  climate. 

Other  factors  also  enter  into  the  problem.  Many 
primitive  tribes  readily  abandon  their  tilled  fields 
and  their  dwelling  places  without  the  spur  of  neces- 
sity due  to  decreasing '\  water-supply.  The  scanty 
supply  of  firewood,  soon  exhausted,  may  enforce 
migration.  Wars,  by  withdrawing  labour,  result  in 
the  neglect  of  agriculture,  so  that  the  land  in  an  arid 
region  reverts  to  its  original  desert  condition.  Irriga- 


(  'A 

CHANGES  OF  CLIMATE  355 

tion  systems  are  vulnerable,  and  are  easily  silted  up 
by  blowing  sand,  or  are  destroyed.  In  Mesopotamia, 
the  neglect  of  dykes  which  had  been  built  to  check 
the  Great  Swamp  resulted  in  a  change  in  the  course 
of  the  Tigris,  and  land  which  the  river  had  rendered 
fertile  became  a  desert.  Former  caravan  routes  are 
abandoned  because  altered  economic  conditions  have 
rendered  them  useless.  Continued  irrigation  usually 
produces  increasing  salinity  of  the  soil,  and  may 
necessitate  the  abandonment  of  cultivated  fields. 
This  cause,  and  also  the  invasion  by  nomadic  tribes 
in  prehistoric  times,  are  believed  by  Fewkes  to  have 
been  more  important  than  possible  climatic  varia-p> 
tions  in  causing  the  abandonment  of  many  ancient 
Indian  settlements  in  the  south-western  United 
States. 

Various  purely  human  controls,  like  those  here 
enumerated,  are  believed  by  many  competent  au- 
thorities to  explain  the  facts  which  have  been  brought 
forward  from  Asia,  from  the  Mediterranean  area, 
from  Africa  and  elsewhere,  as  evidence  of  climatic 
changes  within  historic  times.  There  is  by  no  means 
unanimity  of  opinion  on  this  matter. 

Fourthly,  a  region  whose  normal  rainfall  is  at  best 
barely  sufficient  for  man's  needs,  may  be  abandoned 
by  its  inhabitants  during  a  few  years  of  deficient 
precipitation,  and  not  again  occupied  even  when,  a 
few  years  later,  normal  or  excessive  rainfall  occurs. 
It  is  a  striking  fact  that  the  districts  from  which  comes 
much  of  the  evidence  of  changes  of  climate  within 


356  CLIMATE 

historical  times  are  in  latitudes  in  which  a  slight 
temporary  increase  or  decrease  in  rainfall  will  have 
far-reaching  consequences  'for  human  settlement 
and  human  activity. 

Lastly,  geologic  or  physiographic  processes,  such 
as  elevation  or  depression  of  the  land,  cutting  down 
of  the  outlets,  or  the  silting  up  of  lakes,  the  lowering 
of  river  beds  below  the  level  of  irrigating  canals,  and 
the  like,  in  certain  cases  doubtless  explain  some  of  the 
facts  which  have  been  interpreted  as  indications  of 
climatic  changes. 

It  is  apparent,  on  examining  the  evidence  thus  far 
at  hand,  that  the  fact  of  permanent,  progressive 
changes  in  climate  during  historical  times  has  not 
yet  been  definitely  established.  ^ 

Periodic  Oscillations  of  Climate:  Sunspot  Period. 
The  discovery  of  a  distinct  eleven-year  periodicity 
in  the  magnetic  phenomena  of  the  earth,  naturally 
led  to  investigations  of  similar  periods  in  meteorol- 
ogy. Numerous  and  varied  studies  along  this  line, 
extending  back  even  into  the  seventeenth  century, 
but  beginning  actively  about  1870,  have  been  and 
are  still  being  prosecuted  by  a  considerable  number 
of  persons,  and  the  literature  on  the  subject  has  as- 
sumed large  proportions.  The  results,  however, 
have  not  been  satisfactory.  The  problem  is  difficult 
and  obscure.  It  is  natural  to  expect  a  relation  of 
this  sort,  and  some  relation  certainly  exists.  But 
the  results  have  not  come  up  to  expectations.  Fluctu- 
ations in  temperature  and  rainfall,  occurring  in  an 


CHANGES  OF  CLIMATE  357 

eleven-year  period,  have  been  made  out  for  certain 
stations,  but  the  variations  are  slight,  and  it  is  not 
yet  clear  that  they  are  sufficiently  marked,  uniform, 
and  persistent  over  large  areas  to  make  practical  ap- 
plication of  the  periodicity  in  forecasting  possible. 
In  some  cases,  the  relation  to  sunspot  periodicity  is 
open  to  debate;  in  others,  the  results  are 
contradictory. 

Koppen  has  brought  forward  evidence  of  a  sunspot 
period  in  the  mean  annual  temperature,  especially 
in  the  tropics,  the  maximum  temperatures  coming 
in  the  years  of  sunspot  minima.  The  whole  ampli- 
tude of  the  variation  in  the  mean  annual  tempera- 
tures, from  sunspot  minimum  to  sunspot  maximum, 
is,  however,  only  1.3°  in  the  tropics,  and  a  little  less 
than  1°  in  the  extra-tropics.  There  are,  however, 
long  periods  during  which  there  appears  to  be  no  in- 
fluence, or  at  least,  an  obscure  one,  and  the  relation 
before  1816  seems  to  have  been  opposite  to  that  since 
then.  More  recently  Nordmann  (for  the  years 
1870-1900)  has  continued  Koppen's  investigation, 
using  the  mean  annual  temperatures  of  certain  tropi- 
cal stations,  and  finds  that  the  mean  temperatures 
run  parallel  with  the  sunspot  curve,  but  that  the 
minimum  temperatures  occur  with  the  sunspot 
maxima  (amplitude  0.7°).  This  seems  to  contradict 
the  fact  that  the  sun  is  hotter  at  a  time  of  maximum 
sunspots.  The  latter  difficulty  has  been  explained 
on  the  ground  that  convection  is  most  active  at  a 
time  of  sunspot  maxima  and  that  rainfall  and  cloudi- 


358  CLIMATE 

ness,  both  of  which  are  also  at  a  maximum  with  the 
sunspot  curve,  lower  the  temperature,  especially  in 
the  tropics.  It  is  obvious  that  the  condition  of  this 
matter  is  rather  confusing  just  at  the  present  time, 
and  that  the  relation  of  sunspots  and  terrestrial 
temperatures  is  not  wholly  clear.  Koppen's  latest 
results  (1914)  show  that  the  increase  of  temperature 
noted  within  the  tropics  at  times  of  sunspot  minima 
is  about  1°  Fahr.  higher  than  in  years  of  sunspot 
maxima,  and  becomes  less  and  less  apparent  outside 
the  tropics,  disappearing  in  the  far  north.  These 
investigations,  however  interesting  and  important 
they  may  be  to  astronomers  and  physical  meteoro- 
logists, are  really  outside  the  field  of  climatology. 

In  1872,  Meldrum,  then  director  of  the  meteoro- 
logical observatory  at  Mauritius,  first  called  attention 
to  a  sunspot  periodicity  in  rainfall  and  in  the  fre- 
quency of  tropical  cyclones  in  the  South  Indian 
Ocean.  The  latter  are  most  numerous  in  years  of 
sunspot  maxima,  and  decrease  in  frequency  with  the 
approach  of  sunspot  minima.  Poey  later  found  a 
similar  relation  in  the  case  of  the  West  Indian  hurri- 
canes. Meldrum's  conclusions  regarding  rainfall 
were  that,  with  few  exceptions,  there  is  more  rain  in 
years  of  sunspot  maxima.  This  is  to  be  taken  only 
for  means 3  and  for  a  majority  of  stations,  and  is  not 
to  be  expected  at  all  stations,  or  in  every  period.  Hill 
found  it  to  be  true  of  the  Indian  summer  monsoon 
rains  that  there  seems  to  be  an  excess  in  the  first  half 
of  the  cycle,  after  the  sunspot  maximum.  The  win- 


CHANGES  OF  CLIMATE  359 

ter  rains  of  northern  India,  however,  show  the  op- 
posite relation;  the  minimum  following,  or  coincid- 
ing with,  the  sunspot  maximum.  Many  studies 
have  been  made  of  a  possible  relation  between  rain- 
fall and  the  sunspot  period,  but  the  conclusions  are 
not  very  definite,  are  sometimes  contradictory,  and  do 
not  yet  warrant  any  general,  practical  application 
for  purposes  of  forecasting  the  wet  or  dry  character 
of  a  coming  year.  Particular  attention  has  been  paid 
to  the  sunspot  cycle  of  rainfall  in  India,  because  of 
the  close  relation  between  famines  and  the  summer 
monsoon  rainfall  in  that  country.  In  1889.  Blanford 
admitted  that  the  rainfall  of  India  as  a  whole  did  not 
give  evidence  of  the  sunspot  cycle  in  the  records  of 
the  twenty-two  years  preceding.  More  recently,  the 
Lockyers  have  indicated  that  India  has  two  pulses 
of  rainfall,  one  near  the  maximum  and  the  other  near 
the  minimum  of  the  sunspot  period.  The  famines 
of  the  last  fifty  years  have  occurred  in  the  intervals 
between  these  pulses.  These  writers  believe  that  if 
as  much  had  been  known  in  1836  as  is  now  known, 
the  probability  of  famines  at  all  the  subsequent  dates 
might  have  been  foreseen.  The  latest  study  of  the 
relation  of  rainfall  and  sunspots,  by  Gilbert  T.Walker, 
shows  that  the  coefficient  is,  in  general,  not  much 
larger  than  would  result  from  chance. 

Relations  between  the  sunspot  period  and  various 
meteorological  phenomena  have  been  made  the  sub- 
ject of  numerous  investigations,  but,  on  the  whole, 
the  results  are  still  too  uncertain  to  be  of  any 


360  CLIMATE 

but  a  theoretical  value.  Some  promising  conclu- 
sions seem,  however,  to  have  been  reached  in  regard 
to  pressure  variations,  and  their  control  over  other 
climatic  elements. 

Bruckner's  Thirty-five-Year  Cycle.  Of  more  im- 
portance than  the  results  thus  far  reached  for  the 
sunspot  period  are  those  which  clearly  establish  a 
somewhat  longer  period  of  slight  fluctuations  or 
oscillations  of  climate,  known  as  the  Bruckner  cycle, 
after  Professor  Bruckner,  of  Berne,  who  has  made  a 
careful  investigation  of  the  whole  subject  of  climatic 
changes  and  finds  evidence  of  a  thirty-five-year 
periodicity  in  temperature  and  rainfall.  Bruckner 
began  with  the  long-period  oscillations  in  the  level 
of  the  Caspian  Sea.  He  then  investigated  the  levels 
of  the  rivers  flowing  into  the  Caspian,  and  next  the 
dates  of  the  opening  and  closing  of  the  rivers  of  the 
Russian  Empire,  and  finally  extended  his  study  over 
a  considerable  part  of  the  world,  including  data  con- 
cerning mean  temperatures,  rainfall,  grape  harvest, 
severe  winters,  and  the  like.  The  dates  of  opening 
and  closing  of  Russian  rivers  go  back  in  one  case  to 
1559;  the  dates  of  mintage  to  the  end  of  the  fourteenth 
century,  and  the  records  of  severe  winters  to  about 
1000  A.D.  In  a  cycle  whose  average  length  is  thirty- 
five  years  there  comes  a  series  of  years  which  are 
somewhat  cooler  and  also  more  rainy,  and  then  a 
series  of  years  which  are  somewhat  warmer  and  drier. 
Bruckner  has  found  that  the  price  of  grain  averages 
13  per  cent,  higher  in  the  wetter  lustrum  than  in  the 


CHANGES  OF  CLIMATE  361 

drier.  This  thirty-five-year  period  is  not  to  be 
thought  of  as  being  a  perfectly  systematic  recur- 
rence, in  exactly  that  term  of  years.  The  interval  in  • 
some  cases  is  twenty  years ;  in  others,  it  is  fifty.  The 
average  interval  between  two  cool  and  moist,  or  warm 
and  dry  periods,  is  about  thirty-five  years.  More- 
over, not  only  the  intervals,  but  the  intensities  of  the 
individual  periods  vary.  The  mean  amplitude  of  the 
temperature  fluctuation,  based  on  large  numbers  of 
data,  is  a  little  less  than  2°,  which  makes  it  greater 
than  that  obtained  by  Koppen  for  the  sunspot  period, 
and  it  is  natural  to  expect  it  at  a  maximum  in 
continental  climates.  The  fluctuations  in  rainfall, 
also,  are  more  marked  in  interiors  than  on  coasts. 
The  general  mean  amplitude  is  12  per  cent.,  or,  ex- 
cluding exceptional  districts,  24  per  cent.  In  western 
Siberia  more  than  twice  as  much  rain  may  fall  in  wet 
as  in  dry  periods.  Regions  whose  normal  rainfall  is 
small  are  thus  most  affected.  In  years  of  minimum 
precipitation  they  may  become  uninhabitable,  and 
the  population  may  be  forced  to  move  away,  perhaps 
never  returning,  and  allowing  towns  and  irrigating 
works  to  fall  to  decay.  Slight  fluctuations  in  rain- 
fall are  most  critical  in  regions  having  a  normal 
precipitation  barely  sufficient  for  agriculture.  The 
extent  of  land  cultivated,  and  the  returns  of  agricul- 
ture here  fluctuate  directly  with  the  temporary  in- 
crease or  decrease  of  rainfall.  A  supplementary 
study  of  the  newer  rainfall  observations  for  Russia 
and  for  the  United  States,  as  well  as  for  certain  sta- 


362  CLIMATE 

tions  in  central  Europe  and  eastern  Siberia,  has  given 
Bruckner  satisfactory  confirmation  of  his  earlier 
conclusions  in  the  fact  that  he  finds  a  decrease  of  rain- 
fall over  these  districts  as  a  whole,  beginning  about 
the  middle  of  the  decade  1880-90.  The  time  of  the 
"boom"  in  western  Kansas  and  Nebraska,  and  in 
eastern  Colorado,  in  the  decade  1880-90,  followed 
one  of  Bruckner's  wet  periods,  and  the  collapse  of 
the  "  boom  "  came  when  the  drier  period  advanced. 
Farmers  wrho  went  out  onto  the  high  plains  in  the 
years  of  slightly  greater  rainfall  preceding  the  boom, 
and  who  lost  all  their  capital,  and  more  too,  in  the 
vain  attempt  to  raise  their  grain  in  the  years  which 
followed,  could  with  difficulty  be  convinced  that  the 
climate  of  the  plains  had  not  permanently  changed 
for  the  worse.  The  impression  left  upon  their 
minds,  and  upon  the  mind  of  anyone  who  saw  the 
country  later,  was  one  of  decreasing  rainfall,  unsuc- 
cessful agriculture,  and  financial  ruin.  Within  more 
recent  years,  in  this  same  region  of  Kansas,  with  a 
somewhat  increased  rainfall  during  a  wetter  cycle, 
but  without  any  permanent  change  to  a  wetter  cli- 
mate, the  intelligent  choice  of  cereals  better  adapted 
to  the  soil  and  climate,  and  the  rational  use  of  the 
available  water  supply,  have  wrought  a  wonderful 
change  in  the  aspect  and  economic  value  of  the  state, 
The  following  table  shows  the  characters  and  dates 
of  Bruckner's  periods: 

Warm  1746-1755  1791-1805  1821-1835  1851-1870 

Dry  1756-1770  1781-1805  .1826-1840  1856-1870 

Cold  1731-1745  1756-1790  1806-1820  1836-1850     1871-1885 

Wet  1736-1755  1771-1780  1806-1825  1841-1855     1871-1885 


CHANGES  OF  CLIMATE  363 

Interesting  confirmation  of  Bruckner's  thirty-five- 
year  period  has  been  found  by  Richter  in  the  varia- 
tions of  the  Swiss  glaciers,  but  as  these  glaciers  differ 
in  length,  they  do  not  all  advance  and  retreat  at  the 
same  time.  The  advance  is  seen  during  the  cold  and 
damp  periods.  Supan  has  pointed  out  that  the 
Bruckner  periods  appear  to  hold  good  in  the  south 
polar  regions.  And  Hann's  study  of  the  monthly 
and  annual  means  of  rainfall  at  Padua  (1725-1900), 
Klagenfurt  (1813-1900),  and  Milan  (1764-1900), 
brings  to  light  an  alternation  of  wet  and  dry  periods 
in  harmony  with  the  thirty-five-year  cycle.  It  should 
be  noted  that  Bruckner  has  found  certain  districts 
in  which  the  phases  and  epochs  of  the  climatic  cycle 
are  exactly  reversed.  These  exceptional  districts  are 
almost  altogether  limited  to  marine  climates.  There 
is  thus  a  sort  of  compensation  between  oceans  and 
continents.  The  rainier  periods  on  the  continents 
are  accompanied  by  relatively  low  pressures,  while 
the  pressures  are  high  and  the  period  dry  over  the 
oceans,  and  vice  versa.  The  cold  and  rainy  periods 
are  also  marked  by  a  decrease  in  all  pressure  differ- 
ences. It  is  obvious  that  changes  in  the  general  dis- 
tribution of  atmospheric  pressures  over  extended 
areas,  of  the  great  centres  of  high  and  low  pressure, 
are  closely  associated  with  fluctuations  in  tempera- 
ture and  rainfall.  An  oscillation  of  a  few  hundred 
miles  one  way  or  another  may  mean  the  difference 
between  drought  and  plentiful  rainfall  over  extended 
areas.  These  changes  in  pressure  distribution  must 


364  CLIMATE 

in  some  way  be  associated  with  changes  in  the  gen- 
eral circulation  of  the  atmosphere,  and  these  again 
must  depend  upon  some  external  controlling  cause, 
or  causes.  W.  J.  S.  Lockyer  has  called  attention  to 
the  fact  that  there  seems  to  be  a  periodicity  of  about 
thirty-five  years  in  solar  activity,  and  that  this  cor- 
responds with  the  Bruckner  period.  This  longer 
cycle,  underlying  the  sunspot  period,  alters  the  time 
of  occurrence  of  the  sunspot  maxima  in  relation  to 
the  preceding  sunspot  minima.  He  makes  out 
three  periods  in  solar  activity,  of  between  three  and 
four  years,  about  eleven,  and  about  thirty-five  years, 
respectively.  These  are  related  as  1:3:9. 

It  is  clear  that  the  existence  of  a  thirty-five-year 
period  will  account  for  many  of  the  views  that  have 
been  advanced  in  favour  of  a  progressive  change  of 
climate.  A  succession  of  a  few  years  wetter  or  drier 
than  the  normal  is  likely  to  lead  to  the  conclusion 
that  the  change  is  permanent.  Accurate  observations, 
extending  over  as  many  years  as  possible,  and  dis- 
cussed without  prejudice,  are  necessary  before  any 
conclusions  are  drawn.  Observations  for  one  sta- 
tion during  the  wetter  part  of  a  cycle  should  not  be 
compared  with  observations  for  another  station  dur- 
ing the  drier  part  of  the  same,  or  of  another  cycle. 

Climatic  Cycles  of  Longer  Period.  There  are 
evidences  of  longer  climatic  cycles  than  eleven  or 
thirty-five  years.  Bruckner  calls  attention  to  the 
fact  that  sometimes  two  of  his  periods  seem  to  merge 
into  one.  Richter  shows  much  the  same  thing  for  the 


CHANGES  OF  CLIMATE  365 

Alpine  glaciers.  James  Geikie,  in  Scotland,  has 
brought  forward  evidence  of  several  climatic  changes 
in  post-glacial  times.  Blytt,  in  Norway  and  Sweden, 
finds  some  botanical  evidence  of  four  great  climatic 
waves  since  the  last  glacial  period.  Brogger  esti- 
mates that  a  mean  annual  temperature  between  3° 
and  4°  higher  than  the  present  was  found  in  the  Chris- 
tiana Fjord  in  post-glacial  time.  Lorie,  in  Holland, 
finds  confirmation  of  Blytt's  views.  Gradmann,  on 
botanical  evidence,  believes  in  a  warmer  climate  in 
central  Europe  after  the  last  ice  age,  and  then  a  cooler 
one.  Clough  concludes  that  a  three-hundred-year 
cycle  exists  in  solar  and  terrestrial  phenomena,  the 
thirty-six-year  cycle  being,  as  it  were,  superimposed 
upon  the  longer  one.  Kingsmill  reports  a  period- 
icity of  three  hundred  years  in  droughts  and  famines 
in  northern  China.  And  so  on.  As  yet,  nothing 
sufficiently  definite  to  warrant  discussion  here  has 
been  brought  forward. 

Geological  Changes  in  Climate.  Changes  of  cli- 
mate in  the  geological  past  are  known  with  absolute 
certainty  to  have  taken  place;  periods  of  glacial  in- 
vasions, as  well  as  periods  of  more  genial  conditions. 
The  evidence  and  the  causes  of  these  changes  have 
been  discussed  and  re-discussed,  by  writers  almost 
without  number,  and  from  all  points  of  view. 
Changes  in  the  intensity  of  insolation;  in  the  sun  it- 
self; in  the  conditions  of  the  earth's  atmosphere;  in 
the  astronomical  relations  of  earth  and  sun;  in  the 
distribution  of  land  and  water;  in  the  position  of 


366  CLIMATE 

the  earth's  axis;  in  the  altitude  of  the  land;  in  the 
presence  of  volcanic  dust — changes  now  in  cosmic, 
now  in  terrestrial  conditions — have  been  suggested, 
combatted,  put  forward  again.  None  of  these  hypo- 
theses has  prevailed  in  preference  to  others.  No 
actual  proof  of  the  correctness  of  this  or  that  theory 
has  been  brought  forward.  No  general  agreement 
has  been  reached.  Under  these  conditions,  and  in 
view  of  the  fact  that  practical  climatology  is  con- 
cerned with  climatic  changes,  not  of  the  geological 
past  but  of  the  historical  present,  this  portion  of 
our  subject  may  be  dismissed  with  this  brief  mention. 

Conclusion.  The  subject  of  changes  of  climate  is 
highly  complex.  The  exact  nature  of  the  problem 
is  not  yet  perfectly  clear.  Hence  it  is  not  surprising 
that  there  is  much  confusion  regarding  it.  No  clear- 
cut,  definite,  decisive  answers  can  yet  be  given  to 
many  of  the  questions  which  naturally  arise.  There 
is  even  much  confusion  in  the  use  of  the  word  changes 
of  climate.  What  is  often  spoken  of  as  a  change 
may  simply  be  an  oscillation,  of  longer  or  shorter 
period.  A  difference  obviously  exists  between  a 
permanent,  progressive  change  and  an  oscillation, 
or  periodicity. 

The  occurrence,  in  geologic  times,  of  varying  cli- 
matic conditions  is  established,  although  the  actual 
differences  between  the  climates  which  prevailed 
at  various  epochs  were  doubtless  much  smaller  than 
was  formerly  believed  to  have  been  the  case.  There 
is,  therefore,  no  prejudice  on  the  part  of  climatolo- 


CHANGES  OF  CLIMATE  367 

gists  against  the  view  that  climate  may  also  have 
varied  during  historic  times.  On  the  other  hand, 
changes  of  climate  seem  to  offer  a  very  simple  ex- 
planation of  many  otherwise  puzzling  facts.  There 
is,  therefore,  need  of  great  caution  before  appealing  to 
this  cause  alone.  Every  other  possible  explanation 
should  also  be  carefully  tested,  and  rejected  only  if 
proved  to  be  incompetent  and  unsatisfactory. 

There  is  a  widespread  popular  belief  in  permanent 
progressive  changes  during  a  generation  or  two. 
This  belief  is  not  supported  by  the  facts  of  meteoro- 
logical record.  Abundant  evidence  has  been  adduced 
in  favour  of  "changes"  of  climate  within  historic 
times.  Some  of  this  is  untrustworthy;  some  is 
contradictory;  much  has  been  interpreted  without 
sufficient  regard  to  possible  controls  other  than  cli- 
matic changes.  A  great  deal  of  the  evidence  is  of 
such  a  nature  that  it  requires  critical  examination  by 
specialists  in  physiography,  in  geology,  in  archaeology, 
in  botany,  in  history.  In  cases  where  such  experts 
have  looked  into  the  facts,  there  is  at  present  a 
decided  tendency,  if  not  to  explain  the  facts  in  other 
ways,  at  least  to  hesitate  before  ascribing  them 
solely  to  climatic  changes.  Further,  historians  as  a 
group  are  not  ready  to  accept  a  general  relation  of 
cause  and  effect  between  curves  of  possible  climatic 
variations  and  the  great  accepted  facts  of  historical 
migrations  and  adjustments. 

The  whole  question  is  still  being  actively  debated. 
In  some  cases,  a  complete  dead-lock  seems  to  have 


368  CLIMATE 

been  reached.  While  accepting  the  possibility,  or 
even  the  probability,  of  climatic  variations,  it  is 
clearly  the  general  consensus  of  expert  meteoro- 
logical opinion  that  there  is  no  sufficient  unimpeach- 
able evidence  for  believing  in  permanent  progressive 
changes  of  climate  within  historic  times.  "Not 
proven"  is  the  verdict  of  the  majority  of  climatolo- 
gists  who  have  thus  far  studied  the  evidence. 

There  are  clearly  periodic  climatic  oscillations,  of 
relatively  slight  amount.  An  eleven-year  period 
has  been  made  out,  with  more  or  less  certainty,  for 
some  of  the  meteorological  elements,  but  it  has 
proved  of  no  practical  importance  as  yet.  A  period 
of  about  thirty-five  years  has  been  widely  recog- 
nized, but  it  is  of  considerable  irregularity,  and 
cannot  yet  be  practically  applied  in  long-range  fore- 
casting. Longer  periods,  also,  have  been  suggested, 
but  are  not  surely  established. 

As  to  the  possible  cause,  or  causes,  of  climatic 
variations  within  historic  times,  there  is  no  agreement. 
Fluctuations  in  the  amounts  of  solar  radiation,  the 
effect  of  volcanic  dust  veils,  oscillations  of  the  cli- 
matic belts,  changes  in  the  internal  mechanism  of  the 
earth's  atmosphere — these  and  other  controls  have 
been  suggested.  The  hypothesis  that  climatic  varia- 
tions, both  in  geological  and  historical  times,  were 
probably  the  result  of  an  alternate  equatorward  and 
poleward  shifting  of  the  climatic  belts  has  been 
urged.  Many  diverse  types  of  change  may,  in  this 
way,  occur  synchronously  in  different  parts  of  the 


CHANGES  OF  CLIMATE  369 

world.  According  to  Huntington,  the  chief  basis 
for  this  conclusion,  so  far  as  historic  times  are  con- 
cerned, is  the  fact  that  the  Maya  ruins  in  the  dense 
forests  of  Central  America  seem  to  indicate  periods 
of  relative  dryness  when  the  trees  of  California  indi- 
cate moist  periods,  and  vice  versa.  There  is,  how- 
ever, disagreement  as  to  the  ultimate  cause  behind 
this  hypothetical  shifting  of  the  zones. 

In  our  own  day,  short-period  variations  in  the 
character  of  the  seasons  are  known  to  depend  upon 
changes  in  the  position  and  the  development  of  the 
great  permanent  areas  of  low  and  high  pressure,  the  so- 
called  "centres  of  action"  of  the  earth's  atmosphere. 
Hence  it  is  natural  that  some  should  look  close  at 
hand  for  the  most  probable  cause  of  climatic  varia- 
tions. This  view  was  well  expressed  by  the  late 
Professor  Cleveland  Abbe  as  follows: 

We  may,  in  general,  conclude  that  in  the  present  state  of 
the  globe  and  the  atmosphere,  and  without  any  change  in 
latitude  or  altitudes,  moisture  or  sunshine,  it  is  perfectly 
possible  for  such  combinations  of  winds  to  occur  as  to  give 
us  in  one  century  conditions  favourable  for  rain,  snow,  and 
glaciers,  but  in  another  century  drought,  sand,  and  desert. 
These  alterations  depend  essentially  on  extreme  variations  in 
what  is  called  the  general  circulation  of  the  atmosphere; 
they  are  perturbations  produced  by  its  own  internal 

mechanism. 

/ 

Climate  is  a  great  complex,  and  complete  and 
satisfactory  explanations  of  all  the  facts  will  be 
difficult,  perhaps  impossible,  to  reach.  At  present, 


370  CLIMATE 

indeed,  the  facts  which  call  for  explanation  are  still 
in  many  cases  poorly  determined,  and  the  processes 
at  work  are  insufficiently  understood,  j  Climate  is 
not  absolutely  a  constant.  The  pendulum  swings 
to  the  right,  and  to  the  left.  And  its  swing  is  pro- 
bably as  far  to  the  right  as  to  the  left.  Each  genera- 
tion lives  through  a  part  of  one,  or  two,  or  even  three, 
oscillations.  A  snap-shot  view  of  these  oscillations 
may  easily  make  them  seem  permanent. 

Much  remains  to  be  done  in  the  study  of  climatic 
variations,  not  only  in  the  further  collection,  correla- 
tion, and  critical  analysis  of  the  evidence,  but  also  in 
the  investigation  of  the  human  relations  of  such 
variations.  ^uch_differences  in  rainfall  as  are  .associ- 
ated with  the  thirty-five-year  period  of  Bruckner,  for 
example,  may  easily  affect  the  size,  character,  and 
price  of  crops;  control  the  level  and  supply  of  water 
in  lakes,  rivers,  and  underground;  and  have  im- 
portant relations  to  industry  and  transportation. 
Bruckner  has  himself  shown  that  his  climatic  periods, 
by  determining  crop  conditions,  have  a  marked 
influence  upon  emigration  from  Europe,  and  upon 
immigration  to  the  United  States.  H.  H.  Clayton 
and  Professor  H.  L.  Moore  haye_  pointed  out  truit 
cycles  of  rainfall  in  the  United  States  are  also  econo- 
mic cycles.  For  north-western  Europe,  Petterson 
has  traced  relationships  between  climatic  variations 
in  historic  times  and  certain  important  historical 
and  economic  events  there.  Arctowski  has  studied 
short-cycle  variations  of  temperature,  and  h-  s  !.r;ir«:<J 


CHANGES  OF  CLIMATE  371 

the  movements  of  areas  of  plus  and  minus  tempera- 
ture departures.  The  agreement  between  conditions 
over  broad  geographic  areas  leads  him  to  a  belief  in 
extra-terrestrial  control. 

It  is  clear  that  great  interest  attaches  to  the  whole 
question  of  variations  in  climatic  conditions.  When 
the  facts  of  such  oscillations,  and  the  laws  which 
govern  them,  are  accurately  determined,  long-range 
forecasts  will  become  possible  which  will  be  of  in- 
calculable benefit  to  man. 


INDEX 


Abbe  (C.),  on  changes  of  climate, 
369 

Abercromby  (R.),  on  Mohamme- 
danism and  rainfall,  258-259 

Abscess,  tropical,  of  the  liver,  195- 
196 

Acclimatisation,  203-205 

Africa,  interior,  temperature,  89- 
91 

Agriculture  in  tropics,  239 

Alice  Springs,  Australia,  temper- 
ature, 90,  98 

Amundsen  (R.),  on  Antarctic  tem- 
perature, 163 

Angot  (A.),  on  dates  of  vintage, 
349 

,  on  transmitted  insolation, 

15 

Antarctic,  see  Polar 

Arctic,  see  Polar 

Arrhenius  (S.),  on  cloudiness  by 
latitude,  116 

Arts  in  polar  zones,  333-335 

tropics,  239-241 

Atmosphere,  effect  on  insolation, 
13-16 

Auckland,  temperature,  129,  131 

Australia,  rainfall  of  western,  125, 


126 


B 


Bagdad,  temperature,  39-40,  129, 

131 
Batavia,  rainfall,  105 

,  temperature,  89-91 

Belgica  expedition,  174 

Beri-Beri,  201 

Berlin,  rainfall,  115 

Bermuda,  temperature,  129,  131 

Berne,  pressure,  47-48 

Blagoweschtschensk,     temperature, 

135,  136 

Blizzards,  141,  176 
Bora,  53,  132 
Bowman  (I.),  on  climatic  changes, 

341 

Bronchitis,  211 
Bruckner  (E.),  35-year  cycle,  360- 

364,  370 

Bryce  (J.),  on  climate  and  govern- 
ment, 231 
Buchan  (A.),  on  north  polar  winds, 

169 
Buckle    (T.    H.),   on   climate   and 

man,  222,  231,  274 
Buran,  141 


Calcutta,  rainfall,  85 
Challenger  expedition,  37,  79 


373 


374 


INDEX 


Chamsin,  132 

Changes  of  climate,  338-371 

Characteristics  of  the  zones:  polar, 

151-177 

temperate,  108-150 

tropics,  76-107 

Charcow,  temperature,  135,  136 
Chinook,  310 
Cholera,  196-197 

infantum,  213 

Civilisation    in    temperate    zones, 

272-276 
,    primitive,    in    the    tropics, 

232-235 
Classification  of  climates,  35-75 

—zones,  19-34 
Clayton  (H.  H.),  on  mental  effects 

of  weather,  309  j 

rainfall,    commerce,   and   poli- 
tics, 319,  370 
Climate    and    crops    in    temperate 

zones,  295-298 

—government,  230-232 

— habitability,  224-226 

health,  178-219 

man,  general,  220-226 

man,      in     temperate     zones, 

general,  272-274 

weather    and    military    opera- 
tions, 310-312 

—mental  effects  of,  309-310 

— of  tropics,  76,  77 
Climate,  definition  of,  2 

,  changes  of,  338-371 

,  geological,  365-366 

— ,  monsoon,  44,  46 

— ,  physical,  16,  18 

,  relation  to  weather,  2 

,  solar,  7,  16 

Climates,  classification  of,  35-75 

,  coast  or  littoral,  35,  43-44 

,  continental,  35,  38-42 


Climates,  desert,  35,  42-43 

— ,  marine,  35,  37-38 

— ,    Mediterranean,    58,   62,    72, 

122-134 
,   mountain   and   plateau,   35, 

46-53,    106-107,    149-150,    265- 

271 
Climatic      changes      in      historical 

times,  evidences  of,  339-343 

divides,  mountains  as,  53-54 

elements  and  their  treatment, 


5-7 


)rovinces,  Supan's,  55-60,  73- 


74 


zones  and  subdivisions,  19-34 

Climatology,  literature  of,  3-5 

,  meaning  and  scope,  1 

,  relation  to  meteorology,  2-3 

Clothing  in  polar  zones,  330-331, 

333 

—tropics,  236-237 
Cloudiness  by  latitude,  116 

— in  polar  zones,  172-174 

— temperate  zones,  116-117 

— tropics,  87-88 

Coast  or  littoral  climates,  35,  43-44 
Cold  waves,  141 
Continental  climates,  35,  38-42 
Continents    and    temperate    zone, 

278-280 

Cordoba,  temperature,  129,  131 
Crops    and    climate    in    temperate 

zones,  295-298 

Culture  in  polar  zones,  324-325 
Customs  in  polar  zones,  335 
Cyclones  in  polar  zones,  174-177 

—temperate  zones,  112,  117-120 

—tropical,  263-264 

D 

Darwin  (C.),  on  climate  and  man, 
1M:>,  243,  246,  271,  279-280 


INDEX 


375 


Davis  (W.  M.),  on  Bosnian  farm- 
houses, 290 

,  wind  zones,  30-32 

Death-rates,  tropical,  183-185 

De  Candolle  (A.),  on  plant  zones, 

61,63 

Dengue,  200-201 
Desert  climates,  35,  42,  43 
Deserts,  life  of  man  in  temperate 

zone,  298-303 

of  sand  and  of  snow,  335,  337 

,  trade  wind,  life  of    man  in, 

253-260 
Dexter  (E.  G.),  on  mental  effects 

of  weather,  309 
Diarrhceal  disorders,  194-195 
Diphtheria,  210 
Discovery  expedition,  174,  176 
Disease,  distribution  of,  182-183 
Diseases  of  temperate  zones,  205- 

214 

tropical,  186-201 

Doldrums,  82-83 

Drygalski    (E.    von),    on    rain    in 

polar  zones,   171 
Dwellings  in  polar  zones,  329-330, 

331-333 

—tropics,  235-236 
Dysentery,  194-195 


Eiffel  Tower,  temperature,  49,  50 
Elements  of  climate,  5-7 
Equatorial  belt  of  tropics,  89-98 

forests,  life  of  man  in,  243-251 

Eskimos,  331-335 


Foehn,  53,  54,  167-168,  310 
Fog  in  polar  zones,  172-173 


Food  in  polar  zones,  330,  333 

in  tropics,  238-239 

Forest   clearings,    life   of   man   in, 

287-289 
Forests,  equatorial,  life  of  man  in, 

243-251 
,  temperate,  life  of  man  in,  283, 

287 
Franz  Joseph's  Land,  temperature, 

164 
Funchal,  temperature,  39-40 


Gebelin's  climatic  zones,  30 
Geikie  (A.),  on  climate  and  Scotch 

character,  281-282 
Geneva,  pressure,  47-48 
Geographical  regions,  Herbertson's, 

72-73 
Geological  changes  of  climate,  365- 

366 
Government,    climatic   control   of, 

230-232 

of  tropics,  230-232 

Grinnell  Land,  temperature,  164 
Guyot  (A.),  on  climate  and  man, 

228,  273,  324 


H 


Habitability  and  climate,  224-226 

Hann  (J.),  Klimatologie,  3,  5 

,   on   Antarctic   temperatures, 

163 
,  lightning  at  Maracaibo,  250- 

251 

— ,  periodicity  in    rainfall,  358- 

359 

,  temperature  of  tropics,  79-80 

,  climatic  changes,  363 

Hay  fever,  213-214 


376 


INDEX 


Health  and  climate,  178-219 

Herbertson    (A.    J.),    natural   geo- 
graphical regions,  72-75 

Hildebrandsson  (H.  H.),  on  climatic 
changes,  349-350 

Hilgard    (E.    W.),    on    civilisation 
in  irrigated  regions,  233 

Hilo,  rainfall,  92,  94,  101,  106 

Hirsch  (A.),  on  malaria,  190 

,  plague,  198 

— ,  yellow  fever,  193 

Honolulu,  temperature,  90,  97-98 

Humidity  and  cloudiness  in  .tem- 
perate zones,  116-117 
— in  polar  zones,  172-174 

Hungarian  plain,  cloudiness,  146 

Huntington    (E.),    on    changes    of 
climate,  341-343 

,  on  Kashmiris,  307-308 

Hyetal  regions,  71 

Hygiene  in  the  tropics,  185-186 

of  the  zones,  178-219 

Hygrothermal  types,   Ravenstein's 
68,  70-71,  75 


Iceland,  331 

Industries  in  the  tropics,  239-241 

Influenza,  210-211 

Insolation,         distribution         and 

amounts  of,  8-16 
Ireland    (A.),    on    labour   problem 

in  tropics,  229-230 
Isotherms,  polar,  155-165 
Italy,  rainfall,  126-127 


Jaluit  (Marshall  Islands),  temper- 
ature, 89-91 


Jamestown    (St.    Helena),  temper- 
ature, 90,  97-98 


Kiakhta,  temperature,  135,  136 

Kidd  (B.),  on  civilisation  in  tem- 
perate zones,  275 

Koch  (R.),  on  cholera,  196 
— ,  malaria,  189,  190,  192 

Koppen   (W.),  on  classific 
climates,  60-68,  73-74 

,  hyetal  regions,  71 

,  sunspots  and  climate,  357,  358 

,  temperature  zones,  28-30,  33 


Labour    problem    in    the    tropics, 

229-230 
Land  and  sea  breezes  in  the  tropics, 

86 
Land,  relation  of,  to  temperature, 

36-37 
Latitude,  classification  of  zones  by, 

19-23 
Leste,  132 
Leveche,  132 
Life  of  man  in  polar  zones,  322-337 

— temperate  zones,  272-321 

—tropics,  220-271 
Literature  of  climatology,  3-5 
Littoral  climates,  35,  43-44 
Liver,  tropical  abscess  of,  195-196 
Livingstone   (D.),  on  climate  and 

man,  222,  247-248,  257 
Lockye"    (W.    J.    S.),   on    climatic 

oscillations,  364 


M 


Mackinder     (H.    J.),   on    climatic 
changes,  301 


INDEX 


377 


Madeira,  temperature,  39-40,  131 

Malaria,  188-192 

Malta,  rainfall,  125-126,  127 

Man,  life  of,  in  polar  zones,  322- 
337 

temperate  zones,  272-321 

tropics,  220-271 

Manson  (Sir  P.),  on  tropical  dis- 
eases, 186-188,  189,  193,  212 

Marine  climates,  35,  37-38 

Mawson  expedition,  176 

McGee  (W  J),  on  Papago  Indians, 
299-300 

Measles,  212 

Mediterranean  climates,  58,  62, 
72,  122-134 

Meinardus  (W.)»  on  polar  climates, 
161-162,  167-168 

Meld  rum  (C.),  on  sunspots  and 
cyclones,  358 

Mental  effects  of  climate  and 
weather,  309-310 

Meteorology,  relation  to  climatol- 
ogy, 2-3 

Mexico,  rainfall,  92,  94-95 

Micro-organisms,  climate  and  dis- 
ease, 181-182 

Migrations  in  temperate  zones, 
276-278 

Military  operations,  310-312 

Mm  (H.  R.),  on  Uganda  Railway, 
250 

Mistral,  53,  132 

Mohn  (H.),  on  Arctic  climate,  152, 
157,  159 

Monsoon  belts,  72,  102-106 

,  life  of  man  in  the,  264-265 

Monsoon  climate,  44-46 

Mont  Blanc,  pressure,  47-48 

Mossman  (R.  C.),  on  polar  tem- 
peratures, 162 

Mountain    and    plateau    climates, 


35,    46-53,     106-107,     149-150, 
265-271 

Mountains  as  climatic  divides,  53, 
54 

Mountains,  life  of  man  on,  in  tem- 
perate zone,  303-309 

Mountain  sickness,  46-47 

Muhry  (A.),  rainfall  types,  71 

N 

Nagpur,  temperature,  90,  97,  98, 
103 

Nansen  expedition,  152,  157,  165, 
168,  171,  173,  174,  175 

Nerchinsk,  temperature,  39-40 

New  York,  rainfall,  115 

Nordenskjold  (O.),  on  Antarctic, 
176 

Norte,  310 

Northerners  and  Southerners,  and 
climate,  280-282 

North  polar  isotherms,  155-160 

North  pole,  temperatures,  155-160 

North  temperate  zone,  character- 
istics of,  134-150 

Novaya  Zemlya,  temperature,   165 


O 


Olympia,  rainfall,  137-138 
Optical  phenomena  in  polar  zones, 
177 


Pampero,  132 

Paris,  temperature,  49-50 

Peary  (R.  E.),  on  Arctic,  169-170 

Physical  climate,  16-18 

Physiological  effects  in  tropics,  81, 

183,  2-^1-243 
polar  zones,  214-217 


378 


INDEX 


Plague,  197-198 

Plants  in  polar  zones,  151-155 

Plateau  climates,  35,  46-53,   106- 

107,  149-150,  265-271 
Pneumonia,  210 
Polar  zones,  arts  in  the,  333-335 

,  characteristics  of,  151-177 

,  life  of  man  in,  322-337 

,  physiological  effects,  214-217 

Population  in  polar  zones,  328-329 
Port  Darwin,  rainfall,  92,  94,  102, 

105 

Prague,  temperature,  135-136 
Pressure  in  polar  zones,    165-166, 

168-169 

— temperate  zones,  111 

—tropics,  81-82 
Ptolemy,  climatic  zones,  2,  21 
Purga,  141 


Quito,  rainfall,  92-94 
R 

Railroads  in  temperate  zones,  312- 

315 
Rain  and  snow  in  polar  zones,  170- 

172 
Rainfall     and     Mohammedanism, 

258-259 

,  equatorial  type,  90-93 

in  temperate  zones,  113-116 

in  tropics,  82-86 

systems,  classification  of,  71 

— ,  trade  type,  101-102 

,  tropical  type,  94,  96 

Ratzel   (F.),  on  climate  and  man 

222,  225,  233-234,  262,  278 
Ravenstein   (E.   G.),  hygrothermal 

types,  68,  70-71,  75 
Reindeer,  327-328 


Rheumatism,  211-212 
Ross  (R.),  on  malaria,  189 


Sakhalin,  temperature,  135,  136 

Santis,  pressure,  47-48 

Sao  Paulo,  rainfall,  92,  94-95 

Savannas,  life  of  man  in,  251- 

Scarlet  fever,  212 

Schott  (G.),  on  climatic  chang« 

Scilly  Isles,  temperature,  135,  136 

Scurvy,  217 

Sea  breezes  in  tropics,  86 

Seasons,  effect  on  man,  117 

in  tropics,  80 

Semipalatinsk,    temperature,     135, 

136 

Sirocco,  132,  310 
Sleeping-sickness,  201 
Smith    (G.),  on  British  empire  in 

India,  232 

Snow  in  polar  zones,  170-172 
Solano,  310 
Solar  climate,  7-16 
Southerly  burster,  132 
Southerners  and  Northerners,  280- 

282 
South  polar  temperatures,  160-163 

— temperate  zone,  121-122 
Steppes,  life  of  man  in  the,  289-295 
Subdivisions    of    temperate    zone, 

120-121 

Subtropical  belts,  113,  122-134 
Summer  diseases  of  temperate  zones, 

206-207 

Sunspot  period  in  climatic  oscilla- 
tions, 356-360 
Sunstroke,  199-200 
Supan  (A.),  on  Arctic  pressure  . 
Supan,  climatic  provinces,    5.5-60, 

73-74 


INDEX 


379 


Supan,  rainfall  of  eastern  Atlantic, 

127,  128 

,  rainfall  of  Europe,  126-127 

,    temperature    zones,    24-28, 

32-33 

T 

rate  forests,  life  of  man  in, 
-287 
aes,  characteristics   of,    108, 

— ,  diseases  of,  205-214 

,  life  of  man  in  the,  272-321 

Temperature  in  polar  zones,  152- 

165 

,  equatorial  type,  89-90 

,  land  and  water  and,  36-37 

— ,  tropical  type,  96-98 

,  zones,  24-30,  32-33 

Thorshavn,  temperature,  135,  136, 

140 

Thunderstorms  in  tropics,  86-87 
Trade  wind  belts,  98-102,  253-264 

at  sea,  260-264 

,  life  of  man  in,  253-260 

winds,  83-84 

Transportation   by   water  in   tem- 
perate zones,  315-318 
Travel  and  transportation  in  polar 

zones,  333-335 
Tropical  abscess  of  the  liver,  195- 

196 

death-rates,  183-185 

diseases,  186-201 

Tropics,  agriculture  in  the,  239 

— ,  arts  in  the,  239-241 
,  characteristics  of  the,  76-107 

— ,  development  of,  226-229 

— ,  government  of  the,  230-232 

,  hygiene  of  the,  185-186 

,  labour  problem  in  the,  229- 

230 


Tropics,  life  of  man  in  the,  220-271 
,  physiological  effects,  81,  183, 

241-243 

,  seasons  in  the,  80 

Tuberculosis,  207-210 

Tundra,  characteristics  of  the,  326- 

328 
Twilight  in  polar  zones,  177 

— tropics,  88-89 
Typhoid  fever,  212-213 


Valentia,  rainfall,  116 
— ,  temperature,  39-40 

W 

Wadi  Haifa,  temperature,  90,  97,  98 
Walker  (G.  T.),  on  climatic  changes, 

359 
Water,    relation    to    temperature, 

36-37 
Weather   and    climate    in    tropics, 

76-77 
,  mental  effects  of,  309-310 

— ,  military  operations  and,  310- 

312 

— of  polar  zones,  174-177 

temperate  zones,  117-120 

,  relation  to  climate,  2 

— ,  various  effects  of,  318-321 
Westerly  winds,  111-113 
Whooping  cough,  213 
Winds  and  rainfall  in  tropics,  82-80 

polar  zones,  175 

temperate  zones,  111,  113 

Wind  zones,  30-32 

Winter  diseases  of  temperate  zones, 

206-213 

Wocikof  (A.),  Klimate  der  Erde,  4 
,  on  climatic  changes,  351 


380 


INDEX 


Woeikof ,  on  tropical  rainfalls,  85-86 

,  wind  zones,  32 

Woodruff     (C.    E.),    on    light    in 
tropics,  242-243 


Yakutsk,    temperature,    135,    136, 

140 

Yaws,  201 
Yellow  fever,  192-194 


Zonda,  310 


Zones,  characteristics,  polar,   151- 

177 
,  temperate,  108-150 

— ,  tropics,  76-170 

— ,   climatic,    and    subdivisions, 

19-34 

— ,  hygiene  of  the,  178-219 

— ,   polar,   life   of   man   in   the, 

322-337 
,  temperate,  life  of  man  in  the, 

272-321 
,  temperature,  24-30,  32-33 

— ,  tropics,  life  of  man-  in  the, 

220-271 
,  wind,  30,  32 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 
This  book  is  DUE  on  the  last  date  stamped  below. 


OCT  22  1947 


12Dec'49JQ 


FEB 1  ^  1955  LU 


R^C'D  LD 

71962 


7feb'55 

LD  21-100m-12,'46(A2012si6)41 


NlO'65-apM 
MAR201966  3 


REC'D  LD 

15'66-l.PM 


1C  91180 


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UNIVERSITY  OF  CALIFORNIA  LIBRARY 


